If I get a Netflix card with 15 euro and then start a month for every 10,99 euro, I will get the 3.01 euro back to pay for the next month or will the 3.01 euro expire?
As far as I know the credit should remain on your Netflix account… Possibly. Does it expire after two years or so…
The balance will be used up as soon as you start and the rest will be deducted from your bank account.
If there's money left on your prepaid card, your balance will be kept in your Netflix account. You can then redeem a prepaid card. Then your balance will be added to the new balance.
Unfortunately, you can't withdraw the balance. Your balance will remain in your account when you cancel your subscription. Because your account will not be deleted.