The worst they can do to you is file a lawsuit against you, get a judgment, and never be able to collect a dime from you.
If you give a creditor the authority to draft payments directly from your checking account, then you'll either have to close that account and open a new one or change banks. Sometimes if you lose an account and a draft payment request comes in for a closed account the bank will re-open that account, reject the payment, and charge you $25-$35 for an insufficient funds fee. With payday lenders, they'll occasionally re-attempt a couple times which can run your fees up. In that case, you'd have to change banks.
Traditional payday lenders and title loan companies are just shy of loan sharking - short mostly by not having Vito show up and knee-capping you. 200-400% interest is legal in Nevada for short-term loans and is a financial death spiral.
If you feel some obligation to pay them something, go through what you paid them already and if you haven't paid them an amount equal to their original loan amount then feel free to pay them more if you want. Once you feel you've done what you can then you can just send a letter, via certified mail (solely to prove you sent a letter to them) to the payday loan company telling them that you can't afford to make the payments anymore, that you are retired and judgment proof, and that they are free to sue you if they want but they'll never collect another dime from you.
Then change your phone number and forget about them. They'll probably file a lawsuit against you and get a default judgment against you. But if your bank account never has more than twice what your monthly social security income is, then your bank is required by federal law to reject any bank account garnishments on the account where your social security is deposited into.
William Devine, II
I am an attorney, just not your attorney (yet). Any answers here are to be deemed informational unless and until you retain me as your attorney for actual legal services and legal advice. I offer free in-person consultations so feel free to contact me offline by email or phone. If you like my answer, please hit the thumbs up button.