Need help with payday one in TN

I live in Tn and have a pdl through payday one and have paid them off twice but now have another balance with them.I increased my loan amount with them just to have the money to make their payment and im in over my head.The interest is killing me! I do not have the money to keep paying them.I can only afford to pay them $100 per month but my payment is around $300 per month.My payment is debited by ACH from my checking account and I can't close my account because all my other bills are set up as ACH as well.I like my bank and want to stay with them for the location convienience. My credit is so bad Im also afraid no other bank will allow me to open a new account and the bank Im with already sent one of my accounts to collections for over drafts so It's crucial I keep my remaining account in good standing so I can stay with this bank.It's also unlikely they would allow me to open another account with them so the account I have is it for me. That being said, there is no way I can afford to pay the $300 that is scheduled to be debited from my checking account in the next few weeks from payday one.I don't think payday one is illegal in TN so that won't be a route for me to take.I plan to write payday one and tell them I no longer authorize them to debit my checking account and I can not afford their payment but will be happy to send them what I can afford.Is this what I need to do? if so what should I say in the letter and what other advice should I have before sending my letter? I am self employed so my check can not be garnished if they sue.