Vodacom is *****ing my money

I had my fibre installed by Vodacom years ago, I have been having no issues with them till they suddenly decided to increase my installment from R 600 to about R 850. I called them 2 weeks ago only to be told that they decided to increase my internet speed from 10 up and down to 75, of cause this comes with an increase of about R 250, they just went into my account and took my money without consulting me, no communication whatsoever...they then tell me that the speed of 10 has been discontinued, right?, but they skip 25Mbps which is even cheaper than 10mbps, and 50Mbps because that would have meant lesser commission for someone and they decide to upgrade it all the way to 75mbps????? A week later I still dont hear from them after they promised to take it back to a lower speed and refund the extra money they took from my account ...only to be told that my query was not attended to and they cant refund me because I have already used the higher speed... Like they dont care that I never complained about the speed I have been using for years with no issues, worst part is that my internet was not even faster than it normally is... I then threaten to cancel and they immediately reduce my speed but log a dispute for my refund...almost a week later no feedback on my refund only to receive an invoice today stating that I will again be billed the R850 at the end of this month?????