i’d like my credits balance to get 0€

You’ll either need to spend it or if it’s not enough to purchase a product or service, you’ll need to contact Apple Support to have your account set to zero. If you’re in the US please call 1-800-MY-APPLE or outside the US, consult the support article below.

Choose your country or region - Official Apple Support

Change the language and region on iPhone - Apple Support

Change your Apple ID country or region - Apple Support