Riddle & Associates sent me a letter regarding a debt

My mother recieved a letter at her house in Connecticut for me from this law firm. Stateing that I owe a dept to a credit card company. The amount that they say I owe is more than double what is reported on my credit report. I called the Credit card co. and they told me the account had been handed over to a different company. I have called this company many times and no-one returns my calls. I don't know what to do. Does anyone have any experience with this?
thank you
Amy

Is this company located in Florida?

No they are out of Utah. They are licensed in Connecticut but I could not find anything on them for Florida. I do owe half of the bill and had called the company just a few days prior to my mother recieving the letter.

Call the credit card company once again and tell that you want to make payments towards your accounts. If they have hired this company for collections, they can receive your payments and you won't need to deal with the CA.

Get the address of this collection company and recite the FDCPA laws in a letter and get the debt validated in writing. Make sure that the letter is sent through certified mail and return receipt requested. You need to make sure that this company is doing legitimate collections and has correct details about your accounts.

I doubt that this is a real law office