Insulted by a call centre consultant

On Wednesday the 21 October 2015 I got a call form this number *** at 14:37. The person on the line sad her name was Portia calling from Cell C and mentioning that my name has been selected by Cell C to qualify for a 12 months airtime contract. I told her I was not interested after that she imitated my voice in a very rude way and dropped the call. I was very upset and disappointed at the way i was treated as a potential customer. That kind of behavior should not be tolerated i would like my complaint to be taken seriously.