Amex Credit Card Complaint

Amex Credit card department,

Payoff process California

I paid off my credit card with American Express. It was a check for $6000.00. They cashed the check, but failed to payoff my account. I have a copy of the check they cashed on -/-/16 which was drawn off of - - -. Check number -. Please fix this as I 've contacted American Express numerous times and have gotten no help. At one point they mentioned doing an investigation which would take 30 days. This is unacceptable.