******** deduction from my personal account without prior communcation/changing More than contract amount

I have a Data Contract With Vodacom that commenced in Feb 2019 for a fixed amount to the value of R199 without any communication Vodacom has decided to increase my subscription to R218 since April my contract is a Top up ( once data provided by Vodacom is depleted I have to top up out of pocket and this doesn't affected my monthly fixed payment with Vodacom of R199 )

I have requested from Vodacom to provide me with clarity on why they are ********ly deducting more than what has been agreed on from my account without any prior agreement ,they have instead sent me a list of T&C explaining that they actually have a right to deduct /amend a contract in the middle of it ,they have thus far failed to prove or send proof of this being communicated to be prior April when this billing changes occurred Vodacom is in possession of all my primary contact channels they use them monthly to send me statement and nothing of sort communicating billing changes has been received by me