Citibank Credit Card Complaint

Citibank Credit card department,

Payoff process Minnesota

- 2015 I sent a bank issued check to - - to pay off my credit card, the check was received and cashed -/-/15. The check was never applied to my account! I started calling them weekly as soon as I saw that it was not applied. They told me with each call that it would be investigated and would take - billing cycles. I also sent a copy of the cashed check ( 3 times ), soon after they started calling me DAILY that my account was overdue. I explained the situation over and over for months as I could not get - person to handle this problem. I 've contacted the - which only increased the phone calls, - of them just today! I have called - which - - uses as their bank, and was told by - that - - would have to handle the situation. I have gone to my local - - and spoke to the manager there, no help! I really do n't know what to do, can you help me?