Question about Google Play

The same thing happened to me.
Reported to Digitec it didn't work. 30fr lost.

Well, you're probably not doing anything wrong, so you'll have to fill out the form. I think the reason for this is that credit cards are often used by fraudsters to steal money and make it anonymous (no one can trace who bought a credit card with what money after it has been resold and redeemed in an account) and Google has appropriate security measures. If this doesn't work, I would contact Galaxus support in your place, they can certainly help you.