Sorry about your son. I didn’t hear about that.
Definitely fight them, and tell them to do their worst. It’s not going to be worth it to them to sue you if the amount isn’t that much. It’ll just mess up your credit rating a little if you don’t pay.
I would also do the recording, since they’re not allowed to threaten you like that with arrest and jail time. I bet that as soon as you say “I’m recording this call”, they’ll have a change of attitude.
Also try and get them to send you a letter, then have a lawyer check it out. I used to work for a hospital billing firm and we had a poorly written debt letter that people could sue us for sending to them (even if the debt was correct). Sort of like when a telemarketer calls you after you request to be taken of the list. They sound like a mom & pop debt collector so chances are their letters are not legally correct. I think it was something like a few hundred dollars penalty too.