American Express never ceases to amaze me... mostly negatively.

I have two Amex Platinum FR cards-- the classic Plat and the AFKL one. In November I opened two disputes against Avianca as two refunds on taxes (award tickets) were never credited after 11 months.
American Express asked me to produce proof of purchase, proof of their policy and proof that I was due the money. I provided all of those things and they initiated the dispute. 2 months later the credits were applied definitively as Avianca never replied.

Fast forward to February.
Two more tickets... 3 month delay... no response from Avianca regarding a refund (they say it takes up to 10 months... the truth is that you never know if you will actually get your money back).
I presented exactly the same documentation again but this time I got a letter in the mail with the most ridiculous answer possible.

"Nous tenons à vous informer que nous n'intervenons qu'à titre d'agents de facturations dans ces situations. Vous devrez contacter le commerçant directement pour résoudre ce litige"
In English- "We inform you that we only act as billing agents in these situations. You will have to contact the establishment directly to resolve this dispute".

I mean, really Amex??? So in essence they are saying "we just take our 3%, screw you". Uh, what about purchase protection? Obligations on behalf of the establishment? I myself have accepted Amex in the past and have had to prove the validity of transactions to Amex...

Thoughts here on how best to address this? Aside from saying "look, you already processed an identical claim TWICE two months ago"....

1200€ a year for this kind of ineptitude? I am really p$ssed off.