This just says what they already told you:
“Should the third-party provider fail to correct the issue
and agrees to refund us, we will then refund the Customer”.
I received this response just now:
*Censored for privacy reasons* (Bitrefill)
Apr 14, 21:11 CEST
Hello!
I understand your situation and the frustration, the problem is that Amazon will keep the funds when they block a card like this due to their algorithms being triggered. Which means we have no way of affecting their decision of a refund. If they do not refund us, we cannot refund you.
/*Censored for privacy reasons*
Sounds like you need to wait for Amazon to do the right thing.