MTN, Rather be grateful than annoying

I have a small data package on my MTN contract, due to the fact that they made their offering so poor that when I upgraded my contract and if I want to keep my monthly payment to a smililar amount, I had to reduce the amount of monthly data to very little, but that is fine, as I am mostly on Wifi and I only top-up data when I need to. BUT WHAT IS REALLY FRUSTRATING, is that whenever I buy additional data, I get the endless phone calls from MTN wanting to sell me additional data contract. I will not take adidtional contract. Just stop calling me and be glad that I bought additional data from you to suppliment your poor contract