Citibank Credit Card Complaint

Citibank Credit card department,

Closing/Cancelling account New York

I took a personal loan through my local bank last month ( - ) to pay off - credit cards, - being a bal of $1000.00 on AT $ T Universal card ( Citi Bank ). My bank sent certified check to them, and I received a letter from Citi dated - - stating " The last payment received was $1000.00 and was applied on - - '', but Citi has not credited my acct with that check, and is still showing the bal due and a payment due. I called 3 times last week, they said they would have to start investigation, and needed info from my bank on if/when that check was cashed/cleared. I called my bank, & that check was cleared prior to the letter Citi sent me, I returned calll to City with the info, & my bank will send or fax the info to them. I called Citi today, again, and was told the same thing ... they will have to start an inverstigation, they have no info on that payment, etc. Now, within a few days, I will have to make another payment to overpay the acct, or I will be in default which will affect my credit. I can not understand how they can tell me they have no info on this payment, made by my bank, of $1000.00, when I have a letter in my hand from Citi dated - -, stating that they received it and it was applied on - -! I do n't know how to get Citi bank to apply that payment to that - - - credit card before I go into default, or at all!