Melon charging clients on zero data apps

I have been using melon mobile for a while now. but recently had a situation where my data was depleted and could not access my banking apps. I know for a fact that most banking apps especially Capitec and FNB offer free data charges but why is Melon mobile charging for accessing these apps on the MTN network. and also note that i was very inconvenienced as i could not pay for fuel using my app