Double the bill even though device is settled

I took out a contract with Telkom mobile in October 2013 (R399), a few months ago I asked them telephonically on their recorded lines when my contract is due for an upgrade. I was told that I can upgrade only in August and my contract is finishing in October. So I said to myself I have 3 months in which I can upgrade: August, September and October. I contacted someone in the store and he advised me that if I don't upgrade it will automatically run into a month to month contract (same price). Now its October and I wanted to upgrade but to my surprise I got a bill (R905) for more than double my monthly subscription which is due the end of October. I phoned the call centre and spent 30 minutes on the line with an agent who still don't know what I am talking about (totally useless). Then contacted the call centre again and spoke to someone else who advised me that the R905 is actually because my contract expired the 1st of October and the discounts has been taken away. Included in this contract was a Laptop, Router and Data.