Unsolicited MTN messages

I have had a contract with MTN for many years. Largely they give good service and reception is good in the rural area I live. About 2 years ago I started receiving promotional messages from MTN and promptly unsubscribed from ALL unsolicited messages. About 6 months ago I started receiving these silly messages again and called the call centre. They advised going onto the app and unsubscribing as well as the *141*5# route. I did both and it went quiet again. Now about a month ago I started receiving MoMo messages every second day. I am back to square one. These messages are tantamount to harassment! I am due to upgrade, but am seriously considering moving to another network. I hate being disturbed for nonsense!