STOP spamming me!

A while back MTN absolutely spammed my phone with competition and marketing *******. (Which I never asked for) With quite a bit of effort I managed to stop the spam. Then, probably a year ago, the spam started up again. I have been to the MTN store twice now. I have dialed probably every USSD code that have ever existed. I am running not one, but two MTN apps on my phone because they support different features that needs disabling... And still, you guys are spamming me. Isn't there a law against this? First of all, I never opted in. Secondly opting out is impossible. Not even the MTN staff knows how to stop the spam. On my second visit, one person suggested that I opt out of PRS Communications with the old app. The problem there being... Doesn't matter how many times I switch it off... It stays off for an hour or so, then switches itself on again. Can someone please tell me how to opt out of ALL of your marketing ******* PERMANENTLY. I can not begin to tell you how sick and tired I am of this nonsense. We are bombarded with spam day in and day out, and there is very little we can do about it, but when your own cell company joins in... Unacceptable!