American Express Minimum payment due scam Ft. Lauderdale Florida

I was required to pay minimum payment due of $37.00 at due date.I call them up to pay over the phone 20 days in advence.I did, and representative confirm my payment of $40. 00 as I wanted to pay. But later, checking my Bank account, they took only $30.00 out of my balance. Point is: They wanted to make my balance default, because of lower minimum payment, and charge me high interest rate later. Thanks god I did this 20 days earlier and got checked my account in time.... What would happened if it was last day before due day..
People be careful with these scumy guys.....

Protoword
Clearwater, Florida
U.S.A.