Annoying agents from other networks

Dear Vodacom,

i keep getting annoying calls from ********** and they telling me about paying less for whatever..i can't keep telling them I AM HAPPY WITH VODACOM AND THEIR SERVICES forever..i've been with Vodacom for 10 years, using the same numbe..i still even have the blue sim card so i won't claim someone is handing out our numbers but i wish for vodacom to do something about these people calling on behalf of another network i have no interest in.

Thanks