Terrible Service

Less than 2 weeks ago a Vodacom agent called to inform me that my contract was coming to an end and if I would like to upgrade. At the time I had agreed and however they mentioned that I can cancel within 14 days if I changed my mind. It has not been 14 days yet and I have been trying to contact them telephonically to cancel the renewal but everytime it says they are receiving a high volume of calls and that I should call back. I called at 4 different times in the morning to test the system ( 6am, 7am, 8am, 9am) and received the same message everytime on every number I called..." they are experiencing a high volume of calls and I should try again later". How is one supposed to cancel within the specified time if they get no response at all from Vodacom. I want to cancel my contract!