Vodacom price hacks

Why does companies (like Vodacom) get away with price hacks. Yesterday I wanted to by my son some data (from Vodacom - VodaPay App). First I choose Option - Buy for myself. Price R179 for 18GB - Valid 30 days. Then I choose Option - For another number (my son's). Price R549 for 18GB - Valid 30 days. A price difference of R370 for the SAME amount of data for the SAME period. And at the end of the day, they get away with it. Greedy, greedy, greedy and this from a company that shouldn't be greedy. PS. My son buys more data than I from Vodacom. And the best of all, I'm probably going to get a call from them after this, saying we must review his current package/contract and UPGRADE it to a even MORE expensive package. What a joke.