How to contact someone who has blocked me?

If you have mutual friends, tell them to please let him know that his mom is on hospice, with not many months to live and you just wanted to let him know. Then tell him that he is executor and sole heir, how would he like to be notified when she dies.

Are you sure he is alive?

VBallguy, One more thing I can think of in your case, other than what I said below, is that you are currently POA and you are not able to contact the person who is going to be executor. That means that there will be problems for whomever in the family is arranging funeral services and payment for same after the death of this elder. There will be no right to do that as POA. Any accounts operated as POA or getting SS payments may well be/will likely be frozen until the Executor is contacted, so there will be problems with funeral or cremation payments. If this 94 year old Aunt has instructions, wishes, etc regarding funeral plans and there are funds to pay for that NOW is the time to think about preplanning and pre paying for a funeral out of her funds by yourself as POA.

Just another vote to have the attorney send a certified letter to the son. I can't imagine anyone who wouldn't be curious enough to open it. I don't think the pupose of the letter should be to inform him of his mother's condition -- the purpose should be legal, i.e. his mom's attorney needs to know how to contact him if he's still willing to perform the responsibility of being Executor.

If the attorneys can't locate him or he doesn't open the letter, then I would stop banging your head against this brick wall. When the estate goes into probate, just make sure your mom or you are there to make a claim on it. If the mother passes, and the son remains uncontactable, but changes his mind at some future time, then you'll need a very clear legal paper trail that every effort was made to contact him.

You've gotten some very good suggestions. I'd just like to add a few more, and elaborate on those already suggested.

1. When she does pass and your authority ends, there will be no one to handle Probate unless and/or until her son takes action. So it's a good idea to find a way to contact him now.

2. Given the assets, I would think that any Personal Representative (f/k/a Executor/Executrix) would benefit from having any attorney involved. You might contact one now just to handle the attempted contact, i.e., newspaper publication, but do explain that you have no authority to retain the attorney for probate management as you're not the PR.

3. If you have a copy of the Will, is it done on will paper, i.e., with the firm's name as a vertical border on the left side? If so, I'd contact that firm, including the attorney who probably witnessed the Will.

4. I haven't done this in decades, but I do recall that in my state people who couldn't be located could be notified by publication of a notice in a legal newspaper; I believe the publication ran for several weeks.

I (can't get a typical http citation, but try this:

"Pennsylvania, legal publication notice through newspaper at DuckDuckGo"

It addresses legal notices through publication; I didn't check the statute to see if it addresses other issues, but an attorney could research it to determine if it does.

(I'm assuming that your aunt is in PA as well?) An attorney could also determine whether or not this, or another court rule, could be applied to locate the son now, in anticipation of the need to probate shortly.

Some good law firms might take an assignment like this and have a paralegal handle the issue (at a much lower rate than an attorney would charge.)

5. Better to let an attorney contact him on your behalf since he won't respond to you.
 
6. I would, however, document the attempts you've made so that you're protected in the event that the son can't be contacted or refuses to respond.

I also like Glad's idea of having law enforcement contact him; notifying someone that his mother is close to death would I think be considered to be helpful, just as the wellness checks are.

When Aunt passes you will:
Call the phone number you have and leave a message that she has died and that he is the Executor named in her will.
You will text to the same number.
You will send a letter to the last known address; if it is not returned you will assume he has said letter.
You will contact anyone you know who may be in contact telling them simply that his mother has died. That he is named executor of her estate. That he can contact you for the will and then can go on with his duties.
Your own duties are done at that point. You will have done what you are able to do. You might, if you are still worried, ask an Elder Law Attorney for an hour of phone time to see if there is something else that you need to do.
But as POA you are DONE. There is absolutely nothing you have to do after that.
Wishing you the best.

As POA, you are not responsible for her will as that falls to the executor by default on her passing - essentially, your position is terminated. Place the will into the hands of her lawyer and son will be notified accordingly.
Regarding the imminent passing, did the initial accusation create tensions whereby mother wanted nothing more to do with son? Remember, your role is to reflect her wishes, not make moral decisions. Son has made his position clear, sadly, but if mother showed any signs of remorse then you should endeavour to contact even if it means delivering the news in person (costs incurred through estate if all other avenues mentioned have failed).

This is bread and butter stuff for attorneys - "information to your advantage" letters they can pretty much do in their sleep.

Since he won't answer your calls, just get someone else to use their phone and call, and they can leave a text, voice message; facebook message. Also the registered letter - it doesn't have to come from you, let someone else send it (not the facility, but someone else).

Send him a registered letter without a return address. Maybe curiosity would get him to open it.

If that's not possible because you want the signature card returned to prove he received it, then just send him the registered letter. Chances are he'd read it because he's not obligated to respond immediately like he would with social media or a phone call.

Are there still telegrams? Mail a card?

Do you have a mutual friend, family member that would be shown to get through to him? Police may pay him a visit at your request to let him known what is going on.