Unfair and unjustified price increase

On 27 February 2020, I received an email from Vox announcing "An average increase of 6% will be app**** to the Vumatel FTTH service portfolio effective 1 April 2020." I was paying R599 pm VAT inclusive, yet on 22 March 2020, I received an invoice of R649 payable from 1 April onwards, reflecting an 8.35% increase! I enquired and indicated this was unfair business practice, and received the following response on 29 March 2020: "The Vox product offerings are subject to varying inflationary pressures and your specific basket of services may be higher or lower than the average." I find this response to be completely unsatisfactory. Vox inflated the contracted subscription in a very non-transparent, vague and arbitrary manner. I as the customer was not properly and sufficiently informed of an exact increase, which I believe I was entitled to. The increase was way above the inflation rate. Vox sucks!!!!