Vodacom not keeping up their side of contract.

I did upgrade my Vodacom fiber speed to 80/20 in August 2023, after I did get a good deal from a other ISP also on Frog, So Vodacom said They would give it to me also at R750.00 per month. But every month I have to phone them as they are changing me a very higher amount of R750.00. Last month Warren Heneke from finance said it will be now fixed, but no it is not, again R401.00 extra this month. What must I still do do get this fixed, I want to cancel my contract.