Lack of Upgrade Information is costly

On the 15th July 2019 I went to Zevenwacht Voda Shop to upgrade my existing contract. I decided to go for the Huawei P30 Pro as the monthly installments suits my budget. The person who helped me named Mogamat assisted me with the upgrade. During the time I was there I continuessly asked what will my new installment starting August will be, he then confirmed with me that my new installment will be R765, 98 which I was happy with and then I signed the contract. About a week ago I received an Invoice/ Statement from Vodacom informing me that my new installment will be R1 236,98. I call the customer care service today 12 Aug to find out what exactly the extra cost was. It was explained to me that when I upgraded to a new contract, that the discount I received on the second handsat would fall away and I will pay full fee for the second handset. This information was not communicated to me the day i went in for the new contract. Otherwise I would not have upgraded, seeing that it's going to cost me almost a whole extra R500 a month which I can not afford. I really need a solution as this is concerning that clients don't receive the necessary information to make the right decision financially.