Vodacom Customer care (frustration!)

I've requested numerous times to cancel a data sim card. I've been asked to call a certain number. I've repeated the steps zillions of times and the number is not cancelled. I've tried Tobi without success. After sending an email to customer care, the response email directed me to use Tobi, which I found useless for my request. I've received one phone call from Vodacom, which I've missed since I was busy with a meeting. A voice message stating that they will call again. 10 days later, no follow-up. How difficult can it be to just cancel a SIM card????