Vodacom cancelled my contract on instruction of a sales agent, but has no record of their name?

I had taken a contract (new line) with Vodacom at Game Bayside Mall, in mid January 2018. I had only noticed over the weekend the number does not work anymore. I was advised by the Vodacom Call Centre After sales assistant the Line was cancelled by the Sales Agent. I called Game Bayside Mall cell phone department, and was informed they cant help me over the phone I need to come into the store. I am frustrated, now I need to run around trying to sort out a mistake someone had made. I received a bill from Vodacom for over R1900.00 - its troubling that the only record Vodacom has, is that an (Sales Agent) had cancelled it. They cant provide a name. Luckly I do have the contact details. However, if Vodacom can cancel contracts they should be able to provide customers with a name, as there's not only 1 sales agent. The Sales Agent who cancelled my contract need to take responsibility and active my line, and sort out this mess. With a small baby, I don't have the time to run around and fix a mistake someone else made, and I refuse to pay Vodacom the amount the had invoiced me.