Ongoing Spam calls

I am receiving an enormous amount of unsolicited phone calls from a Vodacom call centre daily from the numbers ********** 296 and ********** 496. I do not answer the calls as luckily True Caller is blocking the calls for me. I do however need to go through copious amounts of voicemails from ******** call centre agents. If you are trying to sell me something... STOP!... or I will be forced to take further action.