Why is this my issue?

I received a call from Vodacom informing me that my account was in arrears. I told the caller that was impossible since I don't have an account with Vodacom. She gave a cell phone number which I have never heard before. She also informed me that I was in danger of being handed over to legal. I left work and drove to my nearest Vodacom outlet to investigate. They checked on their system and all my details were indeed there. The account was upgraded in Alberton in Vodacom 4U. I took more time off to go there and ask for the contract. They informed me they no longer had documents, and their system had crashed, so no records. I again phoned the helpline. I was told that I now have to go to the police station, do an affidavit, pull bank statements, write a letter, get my ID copied and certified, and send everything off to the ***** division. What I'd like to know is, how is this my issue? Surely the onus is on Vodacom to prove that I took out that account? No-one can show me an upgrade document. Why am I having to take countless hours off work to prevent myself from being handed over to legal, when I did not take out this contract??