Mondo bad service

I took out an incorrect data contract with Mondo - my mistake because it was for a home wifi router and not for my phone so I could not use the data. In 2 days time after I received the contract and realize that this was the incorrect contract I canceled it online with the agents. Nevertheless it took you 2 months to cancel the contract and got one big invoice of R 1228.. For a contract that was advertised less than R 200.. Now MTN threatens me with legal action for not paying this account, after sending several emails to Mondo and MtN explaining the issue still nothing has been done reversing this invoice or can give me an explanation why it is such an high amount.