Extra charges on contract

I signed a contract with Vodacom in December 2017 for a Samsung S8+ on the smart top up M+ which is R289 per month plus the device. Should have worked out to R959 per month but since May i see that R45 extra is charged. When i inquired about this i was told that Vodacom informed all smart Top up M+ customers that an sms was send out to inform that all these contracts will be charged with R45 extra and get 150mb more data. Firstly, I was not informed according to my recollection. secondly, my budget allowed for what contract I signed and not for increased costs, irrespective of how small the costs is. I would not have agreed to this. I would like this extra charges to be cancelled from my account as well as the extra data. The past months is done, but for the rest of my contract.