Just to clarify, this policman doesn't exist! Your psycho mother (yes, I did say that), has made this whole thing up. Got a friend to pretend to be a policeman to scare the crap out of you. And it has worked.
Yes, you did the wrong thing using other people's names to set up catalogue accounts. That is fraud. But I don't think anyone could say that you deserve this treatment.
Go to the CAB (if you can't afford a solicitor), ask them what course of action you can take to sort out the mess with the catalogue fraud. If you get that out of the way then your mother will have nothing to hold over you.