Vodacom promotional ****

Vodacom has found a new way of tricking their customers into so-called promotions and then before the original promotion duration expires as signed in the contract, Vodacom one-sidedly and without notification or any type of communication, just stop the promotion and then you have to pay the full amount as if it is not on promotion but a normal contract. We got this promotion when we upgraded another contract and paid R6.99 every month, but now suddenly we have to pay R71.99 as Vodacom decided that the promotion has been stopped. We asked via sms for the upgrade date on that contract on 3 April 202 and received an sms that it can be upgraded on 30 May 2021, which is normally 3 months before the end of your contract. Now they tell us that you can upgrade within 3 months, but obviously at that time it was not the case as it was more than a year. and now they tell us the contract only stops en December, so according to me we should pay that promotional amount until the end of the contract.