This all sounds strange to me: how does it work that you can pay a bill without the electronic payment system telling you what you have paid, i.e. without the phone presenting the amount and asking for confirmation? I don't do phone payments, but any terminal I use a card at always shows me the amount I'll be charged, and nobody can change that after I've authorised it (even if authorisation is just tapping a card on the terminal). But it sounds like you just scanned a code and got a pop-up to say you'd paid: where was the authentication of the amount you had authorised (for that matter, how does scanning a QR authorise it? This goes straight into Google Pay, Samsung Pay or whatever? Do they not show you the amount and ask you to confirm?).
I'm just curious about how this works. As I say, I don't use phone payment systems, so don't know how they work, but am surprised there wasn't an explicit authorisation of the amount that was being charged.