Annoying & Rude Telephone Sales Calls

On Tues, I received a call (number was ***, 19th Oct, 16:10pm) from DSTV Warranty Sale Dept and the caller identified herself as Nonhle. She was trying to sell me decoder insurance or warranty extension on my existing decoder. I told her 'no thank you sisi, i am not interested at the moment'. She then became hostile and rude (asking me how do I know what she was selling etc) with me and hung up the phone. Before she hung up, I said if I wanted insurance, I would have contacted DSTV/Multichoice. Anyway, its disgusting for call-centres to call you (while minding your own business) try sell something and then get rude and hostile with you for not buying. Telephonic sales and call centres are annoying, but I always respect the person on the other side and tell them respectfully when I am not interested. Someone need to teach Nonhle some manners and telephone etiquettes.