If you did get this debt, when did you supposedly aquire it?...What is your states SOL? Most are 4-5 years. If its past your states SOL they can not sue you and at this point they are just blowing smoke to get you to pay. You said that your building a house, so they can see that on your reports and are trying to scare you if your out of SOL. I would keep digging to find out or figure out if its a legit item needing to be paid or if you already took care of it with another company...def need to have that receipt if you can get it. Good Luck
I have contacted the CFPB and filed a complaint as well as my attorney general. I don’t know what good it will do but I just want this madness to stop.
FBI fraud division is also a good contact, this is most likely a scam.