In this case, then our system will treat your transaction as donation, as stated on our FAQ over here: https://bitmixer.io/faqs.html
Then so be it, that's final I guess, People here can't help you with that issue only Bitmixer support can do about it and since Bitmixer owner is not really active on this forum anymore he can't help you either, profile link: https://bitcointalk.org/index.php?action=profile;u=216447