Stick with it. A third party company once erroneously charged my Amex twice, causing my BA 241 voucher to trigger.

I contacted them and they sent me an email stating it was their mistake. I forwarded that onto Amex via their online email system, and they worked with BA to have the voucher removed.

Once I had exceeded the spend on my card, I contacted Amex again, and they got a new 241 voucher added to my BAEC account.

It took a couple of emails to explain the situation, but once Amex understood, it was fairly painless.