Inflated device prices on higher contract packages

Dear Vodacom, I need you to please explain how you calculate your financing options. My mind is absolutely baffled at how, for example, a Huawei MediaPad T3 is priced at 199 on a 4GB contract, but R579 on a 40GB contract. If you look at this mathematically, the price of the data contract should change, not the price of the tablet, the period over which your contract is calculated did not change. Simply put, at a 4GB contract, over 24 months, you pay R109 for data, which means you pay R 90 for the device. But then on the 40GB over 24 months option, you pay R 329 for the data, and R 250 for the device, how can this be right? The finance period of the device did not change, the amount of data per month has, why are you inflating device prices? I have done this exercise as a spot check on phones, tablets and laptops, and in every single case the device prices have been inflated. This is not keeping to the best interest of the client and I feel like CPA is being violated.