Being billed wrong amount for contract

One of my contracts was due for upgrade so I decided to do so. Did a upgrade via the call center at the end of August and all was well or so I thought. I received my new phone but the contract was never changed to a UChoose 350. I phoned the upgrade call center and they said it was rectified but will only apply from the 1st of October. Checking my bill today (29th of september) I noticed I was already billed for the UChoose 350 even though the number is still on a topup 275. This is unacceptable please fix this asap!!