Is it legal to be threatened with arrest

I am disabled and am in the process of filing bankruptcy. A friend called me and said she had a letter delivered to her house via certified mail. She didn't realize it was in my name and her kids signed for it. I had my identity stolen from a so called friend.. Anyway this letter states I will be arrested in 2 days if I don't pay $10,000 .. I've never heard of the collector. I don't use credit cards and haven't in years because of this mess. Anyway..is this legal.and to send it to the wrong address???