Fraud with State Tax Return

I've been getting phone calls from (202)591-1615 on my cell phone (773) 351-4973 for the last four months from a man who says he is with the US Treasury regarding my taxes.  He request that I get in touch with him on the above mentioned number as soon as possible; I could possibly face criminal charges, etc.  Please help me in this matter.  I've already faced identity theft.