Does anyone have an Attorney to deal with BankPlus in Mississippi? They refused to honor my Mom's POA.

I think that, sadly, the bank is doing their job. Unfortunately your mother added your brother to this account. When she dies it is fully his account, and for all intent purpose, if he co-owns this as joint bank account, there isn't a thing on earth that can now be done about this, no matter what the intentions once were as your Mom is no longer of sound mind. If you are representative payee and you have the letter from SS you can transfer now your Mom's social security to go automatically into an account in her name with you as POA. There is nothing else that you can do. It would be as though I am my partner had a joint account and one of his children waved about a POA and said they wanted control over his account, when in fact it is his and MINE. So sorry this happened. Be certain her SS doesn't go into that. I have dealt with POA and Trustee of Trust and SS and IRS for my brother. Al was neat and tidy but it is a pain even at THAT, and you sure do have my sympathy. Sounds like your brother is being uncooperative in this.

What part of the state? I’m guessing it’s not coastal as it’s all Regions, Peep’s or H/W along the i10. So where?
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more importantly, is the POA “springing”? Look carefully at the exact wording on it to see if it needs an additional document for it to “spring” into action & ability to be used.

PoA gets sticky with banks due to fraud and abuse issues. Banks often have their own PoA requirements. Just last month I was visiting my 2 very elderly aunts in FL for whom I am PoA. One is 102 and can barely walk, the other is 99 with advanced dementia and can't walk on her own. My non-demented aunt wanted to add me to their joint bank account and the bank (PNC) said it couldn't happen without all 3 of us physically going to the bank with 2 forms of ID each. Even my aunt with dementia, who would have no idea what's going on. Nonetheless we all went and it was a poop show but it got done.

I believe your brother could not have been added to your mom's account without him being physically present to do so. I'm not sure if the bank can show you the paperwork he would have needed to fill out when he was added. I think every bank's protocol and requirements differ, but they err on the side of extreme caution because in the end, they are liable. Whether you need to consult with an attorney to move forward due to your brother's lack of cooperation is probably a necessary thing. You will need to look online or post a ISO request on Nextdoor.com to find an appropriate attorney for your area.