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After reading your post, I'm assuming your dad is NOT on the debt. If not, the CA made an illegal attempt to serve you. I'm not an expert, however, I can tell you MY experiences with CA's. First of all..don't call them. I would send a letter asking for validation. A CA has so much time to validate a debt with you. Second of all..see if the debt is possibly on your CR. there is such thing as SOL and you need to find out what that is for your state. ALL states have different SOL (Statue of Limitations).
In one of the threads, on this forum, there is information on SOL, etc. for each state. You can 'search' it on the forum and read what it says. Hope this helps you a bit.