Unilateral Contract change

entered into contract with Cell C for home fibre in 2019 and was quoted R699, which I have been paying ever since. I received a statement in May 2021 with a subsequent debit order deduction of R949 When I called Cell C I was told that the service provider in my estate changed from SADV to VUMATEL thus the increase in subscription. I would like clarity on the legality of such a change without my consent. If service providers changed should I not have been given the option of cancelling or renewing? I take exceptional to this unilateral decision taken by CELL C and will certainly register my complaint with the office of the Consumer Protector and Ombudsman

Account Number. ; *** Identity number; *** Name ; Jonathan J Williams Contact numbers ; ***. / ***