I have already tried that some time ago. They only accept cash for top-ups and reloads. Not credit cards or vouchers or stored-value cards.

In Tesco, topping up of TnG is only by cash. Prepaid reloads cannot be purchased using TnG but possible with vouchers. So, buy the vouchers using credit card and use them to buy the top-up.

yes, any cc terminal at payment counter within tesco/giant/aeonbig/etc will be under grocery.

for tesco, usually they don't have cc terminal at customer service counter, so they will bring to one of the empty cashout counter to swipe.

at svc/info counter, yes, i've tried at Giant and Tesco, the first month i gotte Wise card (still adjusting my spending behavior, so gotten vouchers just in case).