I was sold a package their exchange can't support

I was contacted by a Telkom sales person about 4 months back who said that the exchange had been upgraded and that I could now get a faster line speed and more data. The price difference seemed worth it, so I agreed and upgraded. <br> I have had terrible line speeds and many interruptions to the service since then - having to call the call centre at least 5 times in the past three months and losing many weeks without Internet and/or phone service.<br> Then it was suggested to me by a friend to check that I was actually getting the promised 10Mbps because apparently not all exchanges can support these speeds. I checked with Telkom and my exchange doesn't support this higher speed. I am trying to get them to cancel the contract but apparently - even though they can sell you a contract over the phone - I can't cancel one over the phone. I have to go into one of their Direct branches. I am livid as I have had to buy additional data from Vodacom just to stay connected.