NO ASSISTANCE

I have been receiving Airtime request messages from cell number ***. This person sends this message maybe 5 times a day. I am always busy at work and have no time for these kinds of messages, especially since I do not know who this person is. I have tried to contact them via calls, both from my phone and other numbers but they do not respond. I called the MTN customer services on 173 and ecplained yesterday what the issue is and was told to block the number on *121# becvause they might be trying to send me a \please call me". That did not work. I called 173 again today and got cut 4 times before an agent could tell me that they cannot assist me as there is no option to block those messages. she asked if my phone has a blocking option and I told her that I have tried that but the problem is that the message does not come from that number but it comes from MTN and then it shows the message: \""Please send me Airtime. My number is ***.\"" so even if I block the number"