Instruction to cancel contract ignored

I have given notice to terminate my wifi mobile contract on 22. 4.2017. I have been adviced that a penalty will apply for early cancellation and also for the device (router). I carried on to pay the contract fee for 3 months. I have phoned on numerous occassions to get the contract cancelled but no luck. The agent assigned to my case is Charles Legege... He insist that he cannot cancel it as I owe the balance which is currently R3555... I have not used the data sice 22.4.2017. I dont know what to do further.