Incorrect billing and bad customer service

I have a contract with Vodacom that consist of 4 devices. I received my statement in April and I noticed my instalment has increased. At first, I thought the increase was due to airtime which was bought in advanced. I called Vodacom on the 5th May to apply for an upgrade for one of my phones which is expiring the 13th May 2019. I received an sms while on the phone saying that my bill is R 864 for the month of May instead of R 830. I queried this amount and that's when I was told there has been a price increase and that 2 of my devices are affected. Firstly, the one device is expiring and is due for upgrade and Vodacom is increasing the prices instead of promoting the upgrade? how?, secondly, the other one, the contract was taken in November 2018, how is that is due for a tariff increase in less than 6 months since inception of the contract. I have also noticed that, none of my smart top up elements were increased as per "new prices" why? I asked all these question and the agent at the call centre could not answer me at all and opted to escalate the query. I was on the phone with her for 24 minutes and I got no answer, she was cold on the phone and demonstrated no sympathy at all, so I wasted my time speaking and telling her my problem and she did not care at all. I want Vodacom to correct my bill and reverse all charges that they added on my statement. I am very loyal customer of Vodacom and I am paying my account in full and timely on a monthly basis, I do not deserve to be ill-treated like this. I am still willing to give them my business, but they must fix this mess immediately