not sure how to proceed

[Fenris]

I recently recieved a letter from a collection agency (Riddle and Assoc.) for an old cell phone bill. after checking my bankruptcy and finding out they were not listed for some reason, I decided to settle the debt. In the letter, there was a clear statement of a waived fee if paid in 35 days from reciept of said letter, and "Total payment due" was $xxx.xx. I phoned the company and made a credit card paymrnt and authorised them to charge my account for the full amount due. Upon checking my account the next day, I found out I was overdrawn due to them adding on the fee the letter stated had been waived. All attempts to contact the companyand resolve this issue have been met with rudeness and rebuffed. I am not sure if FDCPA applies here, or if it is a matter of fraud through the mails.