Father died in September and social security for August was deposited into his bank account. Bank has held onto this check. What can we do?

Take the probate paperwork to the bank and they'll do what it requires them to do.

Banks are required to freeze the accounts of customers when they learn of their death. There's nothing sinister going on here.

If he died in September he is entitled to the check received in September which is for August. I don't think that is your problem. Did not Probate give you a Short Certificate so you could handle Dads debts and bank accts?

I agree with Glad. And the bank officer should be able to explain to you the freezing of this account. If they cannot you might consider calling medicare/medicaid at 1-800-medicare (you will be on the line a while but they are very nice when you do speak to them) to discuss and ask for explanation.

Was he on Medicaid?

Freezing accounts on death is common. Medicaid may claim those funds as part of MERP, Medicaid Estate Recovery Program.