Vodacom's dishonest business methods

I have 5 contracts on my account, 3 of which are Smart S contracts on a 2 year fixed term basis. On the April 2018 invoices, Vodacom increased the basic contract amount from R236.52 to R260.00(excl VAT) without contacting me or obtaining my authorisation. I spoke to Sikele at their customer service who explained that Vodacom increased our data by 150MB and hence the additional charge. i explained that we never even use all our data in a month and, in any event, use WiFi when at home. We don't need the extra data. Sikele requested I lodge a complaint in writing, which I did on Tuesday 15th May and followed up on Friday 18th May after receiving no response. Vodacom are clearly in breach of contract. Their method of doing business is underhanded, despicable and totally unacceptable. They have not even had the decency to contact me - extremely poor customer service