Cancellation not dealt properly

I went into my branch to cancel my contract- signed the necessary forms and was assured it would be cancelled by the end of May and I would not be billed for June. Furthermore that I did not owe anything else to the company. I have just been billed for this next month because a Telkom Mobile Adviser only contacted me the 15/05 to confirm cancellation- almost 20 days after I had been in store. It's not acceptable to be told one thing and another happens.