MTN Upgrades are harassing me daily.

So I am nearing the end of my contract with MTN and I don't plan on doing an upgrade and I have said this to the call centre agent multiple times. These call centre agents are extremely rude and often put the phone down in my ear when I start to complain. They always know best and are very pushy. I am getting fed up because no matter hownice I try to be and ask them to remove me from the call list but then I just keep getting calls daily. MTN upgrades call centre is a bunch of pirates.