Complaint Review: ACS Incorp

I received an email telling me that I owed over $4000.00 to a company called ACS Incorp.  I did not borrow any money from these people, but they have all my personal information, including my social security number.  They know where I work, and the name of my bank.  When I asked for a copy of the contract that I suopposedly signed, they have not provided it yet.  They claim the original amount of the loan was $300.00. 

They have threatened me with a court appearance, also said they could garnishee my wages, in general, trying to scare me into paying something I don't owe. I am looking into what I can do about this, but from all the information, these people are scammers.