Rude Mtn telemarketers/call centre agents

I have been phoned 3 times by Mtn telemarketers in the past month, each time I have encountered rude and arrogant employees. The moment you tell them you are not interested/already have a contract, they either immediately hang up the call, talk over you or start shouting you for not taking up their service and then hang up before you can ask to speak to their manager. I have never experienced telemarketers that lack the basic telephone s****s and courtesy necessary to phone random people and sell a service to them, Mtn seriously needs to ups**** their employees, disgusting behaviour.