Vodacom Fibre (Changing contract without notifying you)

I am a Vodacom Fibre Client. Their infrastrucutre provider changed their infrastructure to accommodate the lowest line speed to be 80mb/s and not 50mb/s anymore. Without notifying me they changed it to a 150mb/s line. I noticed it on my bill (+- R500) more. When I phoned them, they advise they were forced to do that. I asked multiple times why did they not phoned me but with no answer. They say they are not will refund and that is how it is.