I realize this topic is a bit old (i will also make a post under a new topic), but the exact same thing happened to me recently. I guess I should have looked here before using bitcoinmixer.info, but i did not, and in any case i still feel they should be stopped from continuing their scam.

I have tried contacting them directly, but as i have not yet had a reply or my bitcoins back, i will proceed to contact their hosting provider and anonymity service, to hopefully find out who is behind the page.

Should there be anyone else (having lost bitcoins on bitcoinmixer.info) interested in pursuing this i would be happy to hear from you.