No longer rooted & New SIM

I have a Nexus 4. It was originally rooted when I installed avast anti theft. Since then it has had a few OTA updates, & is no longer rooted. I am not in a position to root my phone again at the moment. But I have switched providers, which means a new SIM card. Since using the new SIM it keeps texting my GF.
How can I stop this, either by making this new SIM acceptable, or worse uninstalling anti theft please.
It is pin predicted (which I remember the pin) & I know the name of the file.
Thanks