Cell C *******ly spamming me with no way of opting out

I am receiving SMSs every day from Cell C all following this format: "Be the first to watch NEW MOVIE TRAILERS and more at only R2/day. Dial *147*6*527# to subscribe! T&Cs. Cell C. To stop reply:out"

Every day I respond with "out", yet I still get them and Cell C charges me for that SMS. Each day is from a different number so blocking the number doesn't even help.

I've contacted Cell C about this and I've also registered on the national opt-out database to no avail. This is infuriating and ******* with regards to privacy and marketing legislation.