Shocking, unexpected R25,000 bill - not mine

I have upgraded my contract in 2013 at a Vodacom shop in Mpumalanga that has been liquidated in the meantime. I asked the attendant to keep my existing cell number, unaware that the phone comes with a promo line/sim card. In August 2019 Vodacom conducted the enormous amount of R16,000 from my bank account. On investigation, they informed me of the promo line that was linked to my name. The Vodacom assistant at the shop called the number and someone else answered on which she confirmed that this was *****. The number was immediately stopped while I was in the Vodacom shop. While at the Vodacom shop, I provided them with 6 months' statements and invoices to proof that I have never received any billing for the promo line up to date. I made an affidavit at the police station on the same day, declaring that it was *****. In Dec 2019, the Vodacom ***** Department notified me that it was not ***** and that I had to pay the R16,000. After several attempt to communicate with them on the matter, there were no replies or service whatsoever. In Feb 2020 Vodacom Customer Care rep****, confirming that it was recorded as ***** on their system. In March 2020 I have been notified by Vodacom that I have been handed over to Legal Collections for R25,000 This is an outrage - I am not in a situation to pay this kind of money as I am unemployed due to a chronic medical condition. I have no idea how to handle the situation as Vodacom is not prepared to help me.