There is no reason why AMEX should honour this when you provided the incorrect KF number in the first place. It appears that AMEX took reasonable action to advise you (on 5/4) considering the magnitude of the issue (low), time to reconcile your account (probably with KF), generate the letter, send it out and finally reach you (within 6 business days) - this is not unreasonable.Transferred points to KF on 3/4 but unfortunately had an incorrect KF number registered with Amex. Amex tell me they "bounced" on 5/4, so 5 days later, they sent me a letter to advise me of this. The letter arrived on 16/4. I am now having an argument with them based on the fact that if they advised me a) promptly and b) via email, I would have been able to make the appropriate corrections. They initially denied my request but I'm having another go.
Yes, I should have checked the number and also checked that the transfer had gone through, but I don't think that excuses their slowly, slowly approach.