75% cancellation fee required.

we were told by assistant at voda store that our data is unlimited. now we find out this isn’t true. we have asked voda to cancel our contract because we require unlimited connection. They are asking for 75% cancellation fee which amounts to 10k. This comes after last year they had to pay penalty fees for this exorbitant % they charge customers as it contravene certain laws. I don’t want to go through the route of asking for assistant from tribunals, icasa etc. how is that Vodacom still charge us 75%? what can I do to have a contract cancelled with them? BE AWARE OF THE 75% cancellation fee.