Call forwarding

So I just got this iPhone XR from some dude the other day and it was fully unlocked and left at the startup page although me being a security freak I wanted to make sure the phone wasn’t tapped or anything to my surprise it was and I was able to check using *#21# and the other forwarding dial codes, so I disabled all the call forwarding features for *#21# but all the other codes still showed it forwarding so I factory reset the phone any nothing still forwarding and it said on one of the codes that it was going to 805-637-7249 so I searched the number up and I got people saying it’s a hacker and others saying it’s T-Mobile so I went with the hacker statements as there were way more so I try all the call forwarding deactivation codes to deactivate it but I keep getting a deactivation failed pop up so I’m assuming this phone has malware and I can’t get rid of it. If there is anyway I can fix this via Apple or using iTunes on my pc it would be appreciated but if this is normal which I suspect it isn’t, then please let me know what I can do and I will leave a screenshot of the error I get.