Still overcharging me for device payments

They have been overcharging me for device payments. On my one contract the device has been paid off since DEC 2014, for my cell phone contract they are still charging me a device fee even though I purchased the device straight up with cash. I have spoken to Trevor about it ***) he admitted to the error and he did give me reference numbers that I will be refunded, task 590776 and task 590780. When I wasn't refunded the next month I called again and spoke to Nichole. ( no reference number this time \just use my name") I am so sick and tired of this company. they just over charge the clients. How they can get away with it I don't know"