Macy's Department Store Paid my account but they said $5.00 past due and have added lated fees up to $186.24, Internet

I paid my account in full.  Then Macy's said I was $5.00 past due and I filed and declared by phone a dispute because what I owed I paid in full.  Macy's charged  me a $37.00 late fee for the $5.00 past due and I disputed that as the account was paid in full. I talked to them in person and they refused to refund the $37.00 

Since then I have faxed them 3 times with documentation that my account was paid in full before the $5.00 late amount was declared by them.  I paid my account in full and currently, 3/16/12, Macy's has me owing $186 the late fee for $5.00 late is charged at $37.00/month because they say I was late for $5.00 on my account. 

Macy's denies that I have disputed these outrageous late fee charges.  I talked to them by telephone, faxed 3 times with all documentation including the check that paid my account for merchandise in full.  I am 70 years old and have only my social security income but Macy's will not stop adding on a late fee month after month of $37.00/month for what they claim was $5.00 late.   I do not know what to do.  Macy's will keep adding on $37.00/month not for merchandise but what they say was $5.00 late on the account and it has been paid in full.  How does a 70 year old woman win against a corporation like Macy's???