fraudulent payday loan

I first got a call last year about a payday loan being taken out in my name, under my SS#. I had to ask what a PDL was because I didn't even know what it was at the time. Needless to say, I was not the one who had taken out the loan. I have been trying to resolve this issue of identity theft even since. National Credit Adjusters was one of the adverse accounts on my credit report, which has since been removed. I called NCA to find out if the issue was resolved and how/why and was told that the 2 loans were sold to other debt collections agencies. So, they were not resolved at all and I'm wondering if this issue is going to continue to haunt me. I received a harrassing call from a debt collector last week claiming to be a law office and saying I was being served and needed to be in court two days from then and I was not sure if it was a scam or what. I have not received anything in writing about this. I am wondering, is it safe to call these collections agencies and give them my social security number while trying to resolve this identity theft? Should I be calling these other companies that NCA supposedly sold these loans to or is that further compromising my security? The alternative is to ignore the situation and I don't see how it will get resolved. I definitely do not want to pay a debt that is not mine so that is not an option.