Overcharge on contract

Hi<br> I've recently upgraded my contract.. The contract was on special but I've been billed the full amount every month.<br> I've queried it and the call centre agents told me they have to pull the call records to confirm amount agreed upon<br> They never get back to me.. It was supposed to be done a month ago..I phoned again 2 days ago and still no feedback..they keep on using one excuse after another...<br> It's ridiculous how *********** the call centre agents are