Vodacom refuse end and change an expired contract

My road with Vodacom probably ends today after 30 years. I'm a recent pensioner. So, my monthly income has dropped significantly. Because of this, I had to stop several things: 1. Medical aid; 2. DSTV; Comprehensive short-term insurance and more. However, I've been battling with Vodacom since November 2024 to change my contract, which has already ended, to a Pay as You go (PAYG), so I'm keeping my old number. From November, I was told by an agent, after calling the cancellation number, that my contract is now been switched to a PAYG. Not so, Vodacom continued to take money from my bank account. As a result, I visited the Vodacom branch in Standerton several times. The branch couldn't help me directly, but from there I'd made contact again with the cancellations department. Instead of helping me to do the switch to PAYG, the agent spends all the time trying to convince me to buy a new contract. I've asked him what I should do, and he told me to stop my payment at my bank. I did so. Since then, I have had a phone call, during which I refused to give my details. Now I'm getting 'reminders' that my account is in arrears and that I must pay immediately to prevent me from losing my number. What is next? They'll probably blacklist me - all because they refused to switch my contract (which has expired Nov 24) to a PAYG.