Norman Bissett & Associates + COJ Billing

Im getting sick and tired of these clowns, I am getting calls from them regarding City Of Johannesburg Accounts unpaid for the past couple of years. I keep on proving to them that these accounts are not mine but that does not stop them calling me again in a couple of weeks or days sometimes, this is disturbing me at work or while I am in meetings.

How do I stop them from calling me ? - My number is listed on their system as a no call but I still get the calls this is disturbing me no end. I have tried to call them and speak to someone but have had no luck reaching anyone.