At some point in the process of purchasing the devices you signed something (whether you were told this or not) that stated that you would keep these devices active on your line with VZW for at least 180 days. The reason for this is because VZW has a 6 month turn around.  The Cellular sales store is paid commission by VZW for selling you the contract and if said contract is terminated prior to 180 days they have to give that money back to VZW. In the Cellular Sales agreement (check the receipts from purchase) this should be explained. Basically they are charging you because they had to pay the money back to Verizon and you still have the devices. They lost money on the deal and that's what they want to make them whole again.