Sorry for what you are going through. Stay strong and you will get through.
We get posts from women in your situation regularly. Because your safety is important, you need to walk away from your current wireless account and phone number. Get a new number with prepaid and pick up a phone. This is the only way to be sure he isn't tracking you.
Do not return the phone from your in laws plan. Remove the SIM card and factory reset. Keep it for calling 911 only. Stash it someplace safe and keep it charged.
Set up the new phone with all new information. Get a new email, change all your passwords.
Wish you luck and safety. 