Telkom false advertising

I have upgraded to a Telkom deal advertised. Upgrade to a 10mbs line and 50Gb date per month at R584. I have had problems before with Telkom, so I phoned and the lady confirmed that this will be the amount I have to pay. But after receiving my invoice they overcharged me and now bill me for R693.99, this is over a R100 p.m more. This is a problem as they call centers are very poor and the hours they are available is during the times I work. I also do not experience anything close to 10m.b speed, closes is about 5m.b s. So now I am paying more for less. They won't let me cancel by them because I have a contract, but they are in breach of contract as they overcharge and do not deliver the speeds the state. I will report them to the National Consumer Commission as this is very unfair and *******.