Xfinity Store -Gaithersburg stole iphones

The Gaithersburg MD xfinity store has stolen two iphones 17 that were supposed to be returned to the warehouse. On Feb 17, we cancelled service and on Feb 18 we dropped off devices but the store has never returned the phones. I will be charged for a service that I cancelled on Feb 17th. Please escalate this higher. I have spoken over 100 times via chat and phone. No one provides any solution. It is very frustrating.