Harassment/Theft

I have been receiving around 20 calls a day, some at night from a No Caller Id. I cannot block the caller as there is no visible number to block it from my phone. I contacted Vodacom, was put through to numerous departments and eventually advised that Vodacom cannot assist and that I should contact the police or RICA (which is an Act not an institution) I went to the SAPS in Malmesbury where I was advised that they cannot assist at all without the number, which must be provided by Vodacom. I then went to Vodashop Malmesbury who advised that I should go back to the police station to get a case number, which I did. I went back to Vodashop with the case number and was then told they cant help me I should download an app - which I cant do as my airtime and data just keeps dissappearing from my phone. I was told then to either get another phone number or maybe approach Apple. Shocking that my service provider cant tell me who is phoning me, surely they MUST know?