Do not worry about it, unless it is a substantial amount they will not bring it to anywhere. Collection agency buy debt in dime for a dollars. If they loose not loosing ton of money. Next time tell them, I have disputed and do not call me again. Once they hear disputed , their best bet is to back up.  Try it , you may not hear a call from them. How ever this collection agency may sell to another party, the mantra is disputed.