Spamming existing customers is NOT ok

I am an existing customer and I have been spammed relentlessly. I receive 6 to 7 calls per day regarding an upgrade. I have resorted to shouting at them on the phone and blocking all the numbers but it doesn't stop. I phoned the Multichoice head office and requested their help but it continued. If they want to know why they are losing subscribers apart from the obvious reasons, this is it. Don't spam existing customers and if I receive another unwarranted call, I'm canceling my subscription.