Presuming that this is one ticket CVG-EZE with a connection at DFW, OP should have been charged whatever was appropriate for CVG-EZE and that is it. While I suspect that the bags were not only overweight, but oversized, OP will need to call AA to ask for a breakdown.

As a caution to others, it's important to get these things resolved at the point of sale. If the agent has it right, there is an easy answer. If not, best to get it fixed on the spot.

Speculation about "baggage" zones and the like is simply not applicable. Neither DOT rules nor AA's own contract work that way. There is a single fee to check the bag (or a bag waiver) + fee for overweight + fee for oversize.

It is also important to know whether OP checked any other bags which did not incur extra fees.