What are my options to stop an automatic debit to Dad's bank account?

Take the POA to the bank. In my experience some banks will honor it others won’t. Don’t use your own money to pay this or even talk to the lender. It’s your dads debt. The lender may have to write it off, but they may try and hornswoggle you into paying it.

This is how I look at it. The $40 is his PNA (personal needs allowance) This money is for his personal needs and the NH holds the account. I would assume you got him down or under the 2000 that was allowed by Medicaid. You can still use that money for him. Ask Medicaid if a loan payment would be allowed against the money left. I was able to pay doctor bills. If Medicaid says no then you need to call the company holding the loan and tell them to stop taking the money out of his account. Explain he is on Medicaid and he has no money. You r not responsible for his debts even as a POA. If there is a house, a lean can be put against it. I am assuming that his SS and pension (If he has one) the NH has been made Payee. Mom had under 200 in her bank account. I asked Moms caseworker if I could close it. He said I could and I did. Main reason was because too many people had her bank info. Maybe u can close present acct and open a new one. You can do this as a POA.

He is still responsible for the debt, I would be trying to figure out how to pay them or return whatever was purchased to create the debt. If he owns a home it made need to be sold to pay off debts and pay for his care until he is at poverty level.

This is probably not what you want to hear, but if he borrowed money it really needs to be paid back, if it is something like a phone contract you can call and cancel, they may work with you, my dad's ex-wife bought a 1000.00 IPhone on his account, because she put everything in his name, I reported the phone stolen and told them that they can work with me to recover the phone or lump it, he didn't have 150.00 a month to pay for the bill. They lumped it, however, because the phone was reported stolen if she went anywhere for service the phone would be confiscated and returned to provider. Good luck getting this all sorted out.

Since Moms SS was direct deposit I never changed her address since she still had her home. Wanted mail to come to the house. When NH became payee they worked with SS and Dads employer with her pension.

He has a home but it has a reverse mortgage against it and Health and Welfare is requiring that we sell the home because he is receiving Medicaid in a different state than his home is located, he lives in sister cities boarding in two different states. Health and Welfare is also requiring that we update his physical address with SS to match to the state he is receiving Medicaid from, probably because his address on file is in a different state. Once we sell the home, if there is any profit I have no problem applying it to the loan, however the loan balance is $8,000 plus and the interest added each month is ridiculous, I'm positive we would not get anywhere close to this in profit after the reverse mortgage is paid off. I'm not sure what he took out the loan for but I believe it may have been for auto repairs to a vehicle that is now non-operable.
My thoughts were along the lines of the reply from Windyridge, I just wasn't sure of doing this because his pension and social security are deposited directly to his bank account. I am new to all this, so I am not sure how the nursing home gets paid for my dad's cost share, all I was told by Health and Welfare was that the nursing home would bill him for his income amount less $40.00. I was also not aware that the nursing home holds this account as JoAnn29 mentioned, I was thinking I could use it to pay for his cell phone to stay active and I would kick in the difference. He seems to do better with answering and communicating with me on his cell phone rather that the one in his room. I also live two states away from him so I want to be sure to keep that cell phone active as long as he still is able to operate it without issues.
Thank you for your suggestions, any other advice is appreciated and welcomed...

Who set up financing with the home. Medicaid requires that SS and pension be paid to the home. When I set up Mom, as POA I allowed the Home to become payee of SS and the small pension she received. I am assuming that when they did this they informed both places that my Mother's address was now the home. I never used Moms PNA account but its been said on this forum that you show receipts where u have purchased items for him and you will be reinmbursed. You will need to call the home and see what you need to do.

I'd seek legal/financial advice from an attorney. It sounds like there are quite a few major issues going on. I'd make sure I was well informed on the options and what is legally prudent on dad's behalf.