contact the credit card company you used to pay the erroneous baggage fees; contest the charges as 'erroneous' (not fraudulent). This is called a 'chargeback'. Send the CC company *all* the documentary evidence you have hsowing what the fee should have been (0). Include descriptive text from website and from your ticketing docs/confirmation.
Done.
Messing around with chasing airlines is a waste of your time.
If your CC has an issue with this service, time for a different CC.