5GB bonus data cancellation

I bought this 5GB bonus and I thought it was a once off thing and it would deduct from my airtime. When I saw that they added it to my account and every month thiey give me that 5GB, I phoned Vodacom in Jan and I asked them to cancel this thing as I cannot afford to pay for it addaed with my contract amount. The guy I spoke to said he has done everything and I will not get this 5GB again. To my surprise again this month, on the 7th February I get an sms that my 5GB bonus data at 50% off has been activated!!!! Who activated this when I cancelled it!!!! Now I am forced to pay for this because it goes to my Vodacom contract account and is debited. Please sort this out, otherwise when my contract ends in March I am cancelling the contract-I will not allow Vodacom t o **** me of my money. I will go other trustworthy networks!!!! Vodacom... Please sort this out!