MTN upgrades harassing calls, refuse to take no for an answer!

MTN upgrades harass the consumer continually phoning for you to take an upgrade. We have told the consultants on numerous occasions, even going so far as to block their numbers, informing them that we are not interested in an upgrade. Their call centre agents are abusive and don't respect your decision not to take an upgrade, and that the only time we will enter into a new contract with MTN is when we personally decide to go to our nearest MTN store to do so.