I bought an IPhone 8plus and after a few months it says no service. It seems like many people have had this problem but?

So I bought an IPhone 8plus from a guy I barely knew(I regret) and after a few months it says no service. It seems like many people on the internet have had this problem as well but my if I go to setting-general-about-network, it's says it is not allowed. I have looked on many sites to see if it has been blacklisted (reported lost or stolen by original owner) and they all say it is clean and unlocked. So I'm just confused, I have reboot it, restored it, got a new SIM card, cut it on and off so many times and it still says no service. It's been about 4 weeks now that it has stopped working and I'm just about to get a new phone from the actual store but I was wondering if I could try another way to fix it before all this money goes to waste.

Call your carrier and ask them to check the IMEI. It's likely there's a balance on the phone that was never paid off and the old owner stopped making those payments. IMEI is different from blacklisted phones so it wouldn't have shown up on your website checks.

I recommend contacting your carrier about this issue.

The MEID has been blacklisted. Your phone is useless, it's likely stolen.