No technical support unless I renew my fibre contract?

I have been a customer of Vodacom Fibre for approximately 4 years. Recently I have had technical problems which take a long time (nearly a week) to sort out. I then gave notice to cancel (30 calendar days which would make my cancellation date 1 January 2026). I assumed that I would be entitled to technical service if I am paying for a service. Immediately after giving notice, my modem stop functioning. I reported the fault which they did not attend to. When I called back they explained that I would only be allowed to replace my faulty modem if I renewed my fibre contract (36 months). If I do not renew, I have to keep paying for the service that I do not get until cancellation. This is a forced sale of an inferior product as I cannot work without an internet connection. Surely this is not legal? Can anyone assist me with this?