Vodacom don't comply with requests from clients and they ignore emails

Vodacom refused to comply with my request IN WRITING to change from contract to prepaid. Then, when my wife phoned on the phone that we wish to change, they refused to comply with the request because for some RIDICULOUS reason, the 'have to speak to me'. UTTER NONSENSE. My wife has full authority to speak on my behalf! how DARE you refuse the request of a client, and also just ignore us?!!?