Handed over to debt collectors for an account I dont have

I canceled my Vodacom account at the end of February 2022. I've asked them to cancel my contract and move me to a pre-paid account. I also made it very clear that I was not interested in taking a monthly airtime/data bundle package.

This past week I was contacted by debt collectors stating that I have an outstanding Vodacom account that has been handed over to them, I tried to contact Vodacom through every number available on their website to no avail. I then contacted the debt collectors to enquire about this outstanding account, I sent through Invoices and Proof of Payment for the last 6 months. The agent then tells me that there are 2 accounts, 1 account is closed and the other has a balance of R600 and my only option to make this go away is to either pay off the debt (for an account I've never opened, neither have I been invoiced for) or go to the store to find out more.

My credit rating is being affected and I cannot get hold of a Vodacom to assist with this query.