Cell C bad service

On 14 May 2018 I took out a new contract with Cell C after being a pre-paid customer for many years. I signed a contract for 2 years for R629-00 per month as this is the only option that you have with cellphone companies. Then the debit order is suddenly R651-15. The person that I signed the contract with, Armond did not inform me that there will be an increase in June 2018 - seems he is not very clued up with contract because several questions he could not answer or said he will come back to me. I do not think he has sufficient training. I would not have signed the contract if he had told me there will be an increase within 30 days of signing contract. This gives me the impression this person is not clued up in what is happening in Cell C. Also had the visit Cell C shops 3 times before anybody could tell me why there is extra billing on my debit order. Seeing that I am a pensioner this is ****ing my budget. I are very unhappy because I feel signing a contract is a binding agreement and cannot be changed as Cell C is doing now. Maybe I should seek legal advise. But be assured we will be the word adverti*****t for Cell C in the country if this matter is not remedied.