How to set Default Card in Apple Wallet?

I have 4 payment cards in my Apple Wallet, a charge card, two credit cards and a debit card. The default card was my charge card. Today I used Apple Pay to make a payment to my energy supplier expecting that the default card - the charge card - would be charged but no the energy supplier managed to select my debit card instead. Within a second my debit card was charged - no opportunity to stop it.

How can this be allowed to happen? I would have thought if my energy supplier did not accept my charge card I would be asked to choose another card.

Is this a glitch in the programming or a loophole nobody’s thought about or what? If this is a legitimate way of using Apple wallet then it ought to be publicised more or have I missed it? (User error 🤔😂)

Anyone got a clue?

[Re-Titled by Moderator]