Constant harassment

Constant harassment from Cell C. I am (unfortunately) a cell c customer. I get calls from them every single day,multiple times to sell me products, offer an upgrade, a new package. I have told them 12 times to stop calling me, to add me to their do not call list and that I am cancelling due to the harassment that I receive. 8 in the morning they call me again. I have asked to speak to a manager multiple times and was denied each time saying "they will note it on the system". Absolutely disgusting