Go buy a prepaid phone that works with your sim card, Turn data on your phone off so its only costing you ~$10/month, visit your nearest truck stop and ask one of the nice gentlemen to drive your phone around the country for the next 3 weeks and then leave it someplace scenic.
In the meantime you can get your own phone on your own plan and get that ex out of your life once and for all, or until you call them again...