MTN is the worst SPAMMER of the all

I have been receiving unsolicited messages from MTN. They come through to my phone at "MTN" no number attached. It is unblockable on my phone and there is no option to unsubscribe. Whe you reply with opt out or Stop you get a message fro "FACTS" and it says not a recognized command and to send "?" to 686. One you do that then you get no reply. I have tried every unsubscribe options available on the internet with no luck. Calling 135 is just as pointless. Every time i get through to an agent, there is this massive delay, that is is impossible to even ask a question. I asked to be called back, with no response. I also keep on getting random USSD options popping up on my phone at random times. I almost subscribe to a service while my phone was in my pocket. This is my last resort, before escalating it legally.