Don't have much to add to the suggestions, switching the SIM to a phone they have never had access to would prevent them from tracking you since they're not using the SIM to track you but a mobile app.

But although they can't track you anymore, that in itself can be a negative. Your parents are most likely expecting a usage pattern from your phone. If you suddenly stop using the phone that has the spyware they will notice that pattern. Be prepared for questions to be raised if they become suspicious. That would really be my main concern, but I also don't see a way around it. Just try to use your main phone somewhat regularly so they're not too suspicious.