I'm sorry I can't say more than you learned an expensive lesson in "too good to be true". The scam is very common and in the time I've been a member of the forum I've seen more than a handful of people coming in as newbies and posting something very similar to what you just wrote.
Even after the police report, you're unlikely to catch them - These scams are usually run abroad. Most legit mystery shopping companies have disclaimers in their front pages against this kind of scam.