Reseting iPhone 6s with iTunes

Solution 1:

You won't lost service with your cellular service provider simply by erasing your iPhone.

However, you iPhone will need re-activation once it is setup again after erasing. Activation process is generally happens automatically.

The iPhone can be erased with or without using iTunes.

TL;DR: Your carrier service is perfectly safe, but you need to know how to enable your phone after erasing it.

Erasing iPhone wouldn't have any impact on your carrier service. As the name suggests, it only erases your data that contained on your iPhone.

However, you mentioned your iPhone is disabled. This one could be a bit tricky. The main question is: Was it locked with an iCloud account?

If YES (which would be true for most iPhones nowadays), you need the iCloud account/password to activate the phone after erasing it.

if NO, then maybe you would be lucky enough to just erasing it and start over clean (losing all previous data of course).