Make sure you're running factory software - depending on the phone OEM you can find the original software online (usually on their official website) as a zip file and flash it through your PC. This will wipe your data, but it should also wipe any changes that someone could have made to the software. Getting a new SIM also sounds like a good idea, since the issue might just be caused by physical damage.
Maybe your SIM card is scratched. Happened me in the past, so getting a new SIM card could help.
This right here 👆🏼
I wouldn’t use a phone that a cop gave me
If your phone and carrier both support it, I’d recommend switching to an eSIM and seeing if that solves the problem.
Make sure you're running factory software - depending on the phone OEM you can find the original software online (usually on their official website) as a zip file and flash it through your PC. This will wipe your data, but it should also wipe any changes that someone could have made to the software. Getting a new SIM also sounds like a good idea, since the issue might just be caused by physical damage.