Vox Telecom price increase only for existing customers

I have an uncapped 10mb/s fibre package with Vox Telecom. My package is supposed to be R803 per month. In January 2019 it was increased to R855.79 and I have been charged that for the past two months. There website still advertised it as R803 and when phoning in there sales department also quotes it as R803, but there accounts department says there existing customers are subject to an increase. The sales consultant first suggested I cancel my package and repurchase it to maintain the price of R803, but there may be some down time. I went through the same experience last year and the price was eventually corrected, but now the same thing is happening again. Why do I need to go through all this trouble just to maintain there advertised price each year and avoid an increase. There is no indication of these inflated prices on there website, nor do there sales consultants know anything about it. So the longer you stay with Vox Telecom the more you end up paying in the long run unless you willing to constantly cancel and repurchase the same product to maintain there advertised price. There vox uncapped voice is also so poor you can barely make out what the other person is saying on the phone. There internet speed is slow and lags when streaming 360p videos. For a 10mb it is running like a 2mb line.