MTN now spamming your outgoing calls

As if the constant SMS's from MTN is not enough, they now advertise on your outgoing calls with a recorded message. I did not sign up with MTN to be spammed and irritated every time I want to make a call. If I want to listen to ****, I will phone someone who talks a lot of ****. I see this as unacceptable business practise and ethics, but it seems it's becoming the acceptable norm these days.<br> Can I therefore ask MTN nicely to stop the harassment, otherwise I will be forced to send them an invoice charging them for advertising on my private number.