Poor practices with regards to Billing

I am a vodacom contract customer and has bought numerous data bundles from them. And last month I accidentally bought a recurring data bundle. Which is not the problem the problem was that while I had airtime the data cost was added to my bill. Nowhere does is state that contract customers pay separate for their recurring data. Which I feel is wrong. I am on this contract because I don't want bill shock at the end of the month.