fashion bug Charging me a finance fee of $75.00 and rising on $23.98 that saleperson didn't process correctly. San Antonio, Texas

I accepted a credit card from Fashion Bug because of and $8.00 savings. I told the clerk that i wanted to debit my bank for the $23.98  before leaving the store. She agreed that I could do that so after she set the credit card up, I slide my card, punched in my pin numbers to pay the $23.98. she said it was all set. and I left.

The next day I came back and bought some more things, total $44.98 and that went through my bank okay.

These transactions took place in Alendale, Ma. I came home to Searsport, Me. a few months later to find letters from Fashion Bug charging me finance charges on the $23.98. I have wrote numerous letters to them explaing the situation but they still havent cleared this matter up and the finance charges continue to rise. They just keep saying, show us where you paid the bill. The problem is that the saleperson screwed up! I dont feel that I should be responsible for her screw-up. I feel that Fashion Bug should waiver the finance charges. What do you think?