Billing/Accounts Incorrectly being Charged

Telkom has charged us for fortfeiting a contract which we never agreed too. All what we did is that currently we were on 2mbps and we phoned Telkom to increase this to 4mbps which they informed us that it will be additional cost per month if we increase from 2 to 4 which we then agreed too. Only after this was done, our Wifi became even slow, and on receiving advise, were advise to go back to the 2mbps as the line itself from Telkom can't at this point handle the 4mbps. On phoning Telkom to change back to 2mbps, we have now been hit with an amount of -R1300,00 plus Vat for cancelling the contract, which in the first place we did not have or were advised that there is a contract in place, hence the fact that we cancelled the contract, which we never did, just merely going from 2 to 4 then back to 2mbps. Then on top of this all, to get someone in Telkom to correct this is another story.