Yes, I have the certificate. It shows my payment as confirmed, but after following the trail, there are unconfirmed transactions on their part.
Who do I send it to, since their support does not respond? I'll gladly PM it to one of you as evidence.
What "trail" are you following? There is no point to follow the money that you sent. Is there an unconfirmed incoming transaction to your destination address(es)?
The user has sent me the letter of guarantee that they've received from Bitmixer. It does verify. Following the transaction trail from his own sent money is indeed pointless as Bitmixer sends the amount from one of their own random addresses. In this case there is no transaction at all from the address specified by Bitmixer in the letter of guarantee to the forward address specified by the user.
Update: The letter of guarantee is not valid. See latest updates.