offerup modem

I did bought a modem/router combo online  from offerup, the modem is certified refurbished or as the guy told me to be. I used the modem from month or so before it stopped working, saying that my service was terminated, and I need to make payment if I want my server backup again.

I did contact the support team letting them know there is some sort of mistake, am up todate with my payment. After few back and forth with the team, we found out that modem was connected to another cox account, and I can't use the modem till it get released or transferred into my account.

I did try to contact the guy i bought it from and I got no answer from him for weeks now.

My question is there way to get the modem working without the other guy or I do have paper weight modem?

Thanks

Hilal Al Harthi