Airtime being ****** from my account and no way to prevent it

I have been a Vodacom customer for nearly 10 years now - I've still always held on to my trusty contract that gives me R200 airtime monthly - I'm not very active on outgoing phonecalls, so I mainly buy a bit of data and I'm easily covered for the month.

In September of last year, I began to notice that I was running out of airtime barely a week into the month. Any topups I bought would vanish in days, no calls being made. Frustrated, I contacted the support desk, who told me to my surprise, that my number was subscribed to premium services ("GLAMOUR BABES" and "FASHION"???) that debited R15-20 per day. They cancelled them for me, and only then I got SMSes to confirm that the service had been stopped. I tried to find out how I had been signed up, only to be told not to click dicey internet ads or SMSing numbers from adverts on late night TV. I hadn't done either of those things, but beyond that they said there was nothing they could do. Fine, I thought, at least it's done.

Then it happened again tow months later. Two more services began leeching my airtime - no confirmation, no opt-in SMSes, nothing. I called again, had them cancelled, again was met with explanation that danced around implying that I was being stupid and careless and signing up for services that cost me money. They assured me I would be notified to opt-in in future.

I've just gotten off my third call on this issue - this month, 3 services (including "Joyous Content"??) were leeching from me. Again, the callcentre agent imp**** it was my own fault, but cancelled it anyway. There's "nothing they can do" to stop me from losing my money. I'm furious and frustrated - Is this how it's always going to be? Why am I even paying for this contract if I can't even use it? From what I understand, Vodacom is supposed to have a secure double-opt in system to prevent this kind of thing, but someone seems to have found a way to circumvent it. My pleas for help are being met with hand-wringing apologies and shrugs.

That's what I get for my years of loyalty. Hundreds of Rands in lost airtime with no solution in sight. At this point the money is better spent buying out my contract and leaving.