Etihad Airlines & American Airlines review: excess baggage fees 2

I booked this ticket through american airlines. the fare rule clearly states below

This is from rdu to cok round trip via lhr and auh. ethihad & american airlines are servicing this route.

Below is the baggage information from my ticket
2ndchecked bag fee-cokrdu-usd100.00

But, we were charged $320 in cochin airport by ethihad.

On aug 04, I called ethihad customer service to inquire about extra baggage fees. I was informed that it is american airlines ticket and I should speak to american airlines. I did get it confirmed by american airlines on aug 04 and today (aug 05), after I was charged $320. they clearly say that it should be $100 only.

I emailed this information to ethihad and followed up again today. they still claim that it is 320$ for excess baggage fee.

Below is the text from my ticket email:
Baggage information

Baggage charges for your itinerary will be governed by american airlines bag allowance - rducok-01 piece/ american airlines /up to 50 lb/23 kg and up to 62 linear in/158 linear cm bag allowance - cokrdu-01 piece/ american airlines /up to 50 lb/23 kg and up to 62 linear in/158 linear cm 1stchecked bag fee-rducok-usd0.00/ american airlines /up to 50 lb/23 kg and up to 62 linear in/158 linear cm 1stchecked bag fee-cokrdu-usd0.00/ american airlines /up to 50 lb/23 kg and up to 62 linear in/158 linear cm 2ndchecked bag fee-rducok-usd100.00/ american airlines /up to 50 lb/23 kg and up to 62 linear in/158 linear cm 2ndchecked bag fee-cokrdu-usd100.00/ american airlines /up to 50 lb/23 kg and up to 62 linear in/158 linear cm additional allowances and/or discounts may apply