Product: Credit card

I was unemployed and unable to pay my monthly amount due on my USAA credit card, so I called them on XXXX XXXX, 2016 and was able to work out a payment plan, which I received payment coupons for and have been paying since XXXX 2016. On XXXX XXXX, 2016 I started receiving letters demanding immediate payment of amounts I could n't afford ( on this date, for {$890.00} ) ; this letter even mentioned at the bottom contacting them about programs they offer to help me clear this debt. I copied the letter and, with the scheduled XXXX coupon, mailed it to them, with copies of all the other payment coupons through XXXX 2016 to show that I 'd already made arrangements to pay on this debt. I never heard anything but on XXXX XXXX, 2016 got another " demand '' letter stating I needed to pay {$1000.00} immediately, but knowing I 'd already mailed them proof that the payment agreed upon was scheduled, I ignored this letter. On XXXX XXXX, 2016, I received another letter stating they had sent me several messages about the account 's past due status and that is was more than 90 days delinquent! This one asked for a payment of {$1100.00} IMMEDIATELY and state that, because of this, the account was closed ( I 'd hoped by having these arranged payments I could save myself from preventing this happening and keep the account open due to the low interest rate of 8.9 % ). This letter was sent AFTER the agreed upon payment set in XXXX 2016 had already been paid as scheduled! At this point I again called USAA on XXXX/XXXX/16 ( I had been out of town for several weeks ) and spoke to XXXX XXXX, supposedly of the Executive department of USAA 's Debt Solutions, and explained all this to her. She said she 'd look into this, but that the payments I agreed to were too low and that 's why the letters were sent. How can I be held accountable for a mistake someone in THEIR department made in the beginning when I talked to this department back on XXXX XXXX, 2016? Also, there was no way I could have paid more, being unemployed, then underemployed at the time. 
I have not heard from anyone since, but just had my credit union account debited TWICE from USAA on XXXX/XXXX/2016, one for a payment of the originally agreed to amount of {$120.00}, for which a reminder letter was sent out on XXXX XXXX, 2016. Then on XXXX XXXX, 2016, I got another letter showing the initial contact date of XXXX XXXX with a payment due on XXXX XXXX of {$120.00}, so I thought this meant they had raised the amount due to {$120.00} ( and this was the only " contact '' I received, this letter with the new amount - no one ever called to tell me this, nor were any documents online in USAA to tell me about this, or any other decisions that had been made ). More confusing is that I also received another letter dated XXXX XXXX, 2016 that showed a contact date of XXXX XXXX, 2016 with a payment due date of XXXX XXXX, 2016 for {$120.00} - very confusing! But they debited BOTH amounts on XXXX XXXX WITHOUT AUTHORITY to debit BOTH! So, I am now incurring insufficient fee charges and ca n't pay other bill since they took out {$240.00}, unbeknownst to me, and which I could n't afford! 
Dealing with them has been a nightmare, and after this event, it is time to make a formal complaint and involve an outside agency. 

Thank you!