Harassment in cold calls

I got a cold call from onair, I had to prompt them multiple times to identify themselves while they kept insisting on me confirming my name.

Once I did they started the sales pitch. I interrupted and said I was not interested. To while I was rudely told that I had not given them a chance to explain the offering. I said I know I don't want dstv, to which I was again rudely told that I'm not giving them a chance, with a raised voice.

It's madness that I tried to politely decline a cold call sales pitch and was met with aggression from the staff.

This is harassment and I want to know how onair got my details and if it was legal. Because I did not consent to this.