Vodacom ****

I recently received calls from vvm debt collectors. They say that they are calling regarding my vodacom account. When I ask the consultant which account is that cos I don't have any account with vodacom then they hang up. I called the number back to enquire about the account since I don't have an account with vodacom. So they said that I am owing vodacom, I have a contract with vodacom.. mind you I have been using my prepaid Sim for more than 10 years and I have never had a contract with vodacom. They said that I have received a device with a contract Sim. When I ask what device did I receive and to which address, what package did I take and when did the contract start, what is the number that's on the contract, who signed the contract, when, and what account number is provided there, they said they don't know,I must provide them with my ID copy so that they can investigate. I don't have a contract with vodacom and I don't wish to take contract with vodacom cos I know that their network is bad at times and data is very expensive but doesn't last. What **** is this? What device did I receive, to what address and how much is the installment, when did the contract start? Then who was paying then defaulted? Where was the contract taken? Who did they inform