Total lies

So May 2017 I called in to cancel my data contract with Vodacom as contract was ending. Rententions called me and asked why I want to cancel on which I said I had WiFi at home and wanted to use that money towards data on my phone. So he said he can offer me that I downgrade to 500mg per month and then he will add 5 GIG per month to my phone free of charge. I asked why he said they wanted to retain my business and that would also keep me as a client come 2018 when my cellphone contract comes up for renewal. Then said he would add it for 12 months so I agreed. Then as he was processing it he said his unable to do so he can only add it for 24 month free of charge. So I laughed and said ok that's fine. I asked him come upgrade time I will keep that data he said yes mam we are trying to keep you on as a client. Now I want to upgrade they say no I will lose the data. This is unacceptable. I was told I would get it for 24 months even if I upgraded. Why would I keep that other contract in place if this was given. I want to upgrade and this data better come with my contracted as promised.