Opt out impossible

The opt out for marketing stuff simply does not work, I have dialled the number provided and followed the steps as well as downloaded the app to unsubscribe AND gone into a branch for assistance. Still I get these sms’s. Please make them stop :(

You've received FREE 300MB data valid for 5 days! Download the MTN App to check your balance and receive exclusive special offers: T&C's apply. Optout? Dial *135#