Poor service experience when cancelling contract

My wife has had cellular contract with Vodacom for many years and finally we made the decision to cancel. She contacted them well advance to confirm the cancellation process. Being the stickler for detail that she is she called many times after that just to be sure and followed up after she submitted that cancellation request to confirm that it in deed it had been cancelled. Only to discover that it has not been cancelled and what's more according to Vodacom there is no record of such call ever been made despite the fact that she took record of the call and each agent that answers confirms that they are processing the cancellation when in fact nothing is being done. This is unacceptable. Part of a good service experience is having the freedom to enter into an agreement and not be pushed to your wits end to cancel that agreement!