Mtn giving out our cell numbers to Telemarketers

I just received a call from telemarketers saying that they received my cell number from my service provider (Mtn). I was so annoyed!!!!!! I have been with Mtn for as long as I have had a cellphone and am so irritated by this. I am not sure why it hasnt occured to Mtn that if I want a certain product, I will go out an look for it, not the other way round. I am even contemplating moving to another service provider in order to avoid these reckless marketers!!!! Is there anybody else suffering the same thing as me? Is this even allowed to happen? Isnt this also part of reckless lending? Someone please help and rescue us from Mtn.