Unable to cancel MTNPLAY

I've been subscribed to MTNPlay without authorisation, but here's the problem - The USSD code they provide to opt out doesn't work, and the website provides an error looping back to enter phone number. And according to the call centre agents, they can't resolve the issue. My emails are also not responded to.

" Yello! Thank you for subscribing to Gravel Road @ R2.02/day. 1st day FREE. Watch now http://bit.ly/2AbvFIR .Use your 2 FREE SPINS and WIN. Dial *156*083# or http://bit.ly/MTNS_W . To opt out dial *464*970#. Ts&Cs mtnplay.co.za For support dial 135. "

And don't bother trying to speak to a supervisor - initially they said they couldn't, then put me on hold for 30 min, very funny you ****holes