Field Code Results CONCERNING

If you feel that you are being threatened, continue working with the police. If they feel it is appropriate, they can arrange for a forensics expert who has access to actual, useable information.

There is nothing other end users here can do beyond reiterating that iPhones are very secure and that it is highly unlikely (as in darn near impossible) that your hardware has been compromised.

I would say that screenshot means your carrier doesn't provide information based on dialing that number. Whether or not you get comprehensible information from field codes depends on your carrier. Not all carriers will provide information on all codes. Some carriers don't allow it at all. I just get an automated message that says my call can't be dialed. Keep in mind that these codes were never intended for the end user.

Calls drop. That can be the result of your carrier's network, it can be the result of transient local interference or, it can be a hardware issue.

Unless your phone has been jailbroken or you are a high-profile activist, journalist, or politician whose data is worth hundreds of thousands of dollars to acquire, the likelihood that your phone has been compromised is as close to zero as to not be worth considering.

Your device is not being hacked; that's improbable.

Try the FBI? Especially if there are interstate calls involved at any point.