Discovery harrassing customers with marketing related calls

I started receiving calls from Discovery to make an appointment to see one of their financial advisors. Every time they call, I firstly advise them that I am not interested in their service and then I ask them to remove my number from their system, as I travel abroad often and then I have to pay the international roaming fees for the call. I am a customer of theirs, being a member of the medical aid scheme, but have never given permission to use my number for promotions or any other marketing. They obviously don't care, as the frequency of the calls are actually increasing.