The mod seems to have misread your problem. Your problem is not that support is not answering and you wanna know why. Or is it? That would be in the rules of this category. (You did write both in one sentence though).
Regarding your problem. Is your debit card supposed to work online? Is it working for other stores online?
If the same brand previously worked on Itch, maybe your configuration was changed by accident.
Itch uses Stripe for dealing with debit cards. So I doubt Itch support can help much there. It is a thing between Stripe and the bank that issued the debit card.