I have the same issue in the US. Tried multiple cards (debit/credit/bank card, 2 different visa gift cards), confirmed funds, etc. What ultimately allowed me to move forward was switching from my bank card to my credit card. For some reason, it seems to have issues processing against any form of bank/debit card, even if that card allows you to run it as credit. Same issue when trying to adds funds from a gift card.
And sadly, Blizzard support was useless. All they did was send me the help article, which I had already tried exhaustively in my own troubleshooting before reaching out to them.