Retention at my unnecessary expense

I have a WIFI Router with Vodacom and when I call to cancel it due to the fact that I cannot afford it anymore because it is slow and worse Vodacom has no Fibre connectivity in our area and I opted for a cheaper Fibre with open serve, which is cheaper and 3x lesser than Vodacom. Vodacom refuses me to cancel it and that makes no sense to keep it (Vodacom) yet I have a cheaper Fibre.