PRA calling about litigation

Hey all, I've been getting calls from these guys for months now. I finally gave in and talked to one of them. They said I was in litigation in California. I'm in a job that only lets me bring home 400 a month and I have a child to feed. I just can't pay these guys. What do they mean by me being in litigation. I asked that they stop calling me and he rudely went on that I can't just ask them to do that. I told him to stop again and that if they didn't I would report them to the proper agencies. his response was "any reports you make won't mean jack crap". I stupidly gave him me new address before any of this went down. (They start off being very polite...) I know the SOL is not up, what can I do other then send a letter to verify the debt. They say I owe 6800 but i know that originally it was much less. I read somewhere, don't remember where, that I can demand a receipt of purchase for the account. Meaning they show proof of how much THEY paid for the account and to work from there to pay that amount off. Funny thing is the phone number they call me at isn't even under my name. It's part of a family plan which is under my mother-in-laws name. They also call and leave messages repeatedly on my sisters home phone. Is that legal? Thanks!