phone shipping error

Went to Xfinity store April 10 to purchase a phone. Was not in stock so the placed order. Met FedEx at my door on April 11. Opened box April 12 and cheaper phone inside. (Not the one I ordered) Have talked to 25 mobile care members and get different answer each time. Was told I would get shipping label to send phone back but never did. Service rep confirmed phone I received was still showing in their warehouse. So I assume someone in fulfillment stole my phone and replaced with cheaper one. I finally sent the phone I received back to fulfillment center per rep and she called be back to get ups tracking number. Said when the phone confirmed back in warehouse, would be able to remove payments from my bill. Was able to confirm phone in warehouse May 12, but still being billed for phone I didn't receive. I can't get another phone activated on this line since it still shows payments remaining. My son's phone is going to quit working while I'm waiting for this to be cleared up. Please assist