How do I stop them from calling me?

I have never been interested in banking with Standard Bank. I can't recall ever sending a message or making an enquiry regarding any of their products. I AM EXTREMELY HAPPY WITH BANKING WITH FNB.

Last week, the first call came from Standard Bank trying to sell me something. I politely asked the caller to put a note on the system to never call me again as I will never be interested in any of their products / services.

Since then, I had 6 calls from Standard Bank call center. How do I make them STOP?