Amex Credit Card Complaint

Amex Credit card department,

Overlimit fee Utah

My mother has an Amex - credit card. She has a $6000.00 limit. She 's had it since -/-/2000. She pays it off in full every month. In early - she had home repairs done and it put her $3400.00 over her credit limit. The payment was not declined because it went over the $6000.00 limit. She received the statement and she paid off the amount in full. She just received her next statement and there is a $54.00 interest rate!! What is that?? After talking with some people, I 've been told this is the interest charge for the $3400.00 that was over the limit - If this is an over limit fee '' why is n't it called that on the statement? And why did n't they decline the charge if it was over the limit?? I think this is an appalling fee that does n't make any sense - except to rip off the consumer. They still made money from charging their credit card fees to the vendor - why do they have to charge an Over Limit fee, especially when everything is paid off immediately??