And just as further information:
If you enter the PUK code 10x wrong, your SIM card will be blocked indefinitely and it will be impossible to unluck it. You will then need a SIM card replacement!
As @Mav1976 already wrote, you can find the PUK:
a) on the documents you got the SIM card with (usually either on that plastic card that you broke the SIM out -or- on the letter that includes this plastic card or the eSIM QR code)
b) on Mein Vodafone if you registered your contract there (as far as I know, you would have to use either the PUK or the customer password to authenticate it)
c) calling the customer care (where you also need your customer password and phone number for authentication)
Option c) might be the only one available to you if you neither have the documents available, that you got your SIM card with -and- you didn't register your contract on Mein Vodafone. The phone number to call would be either +49 172 12 172 12 (for post-paid tariffs) -or- +49 172 229 0 229 (for prepaid tariffs like CallYa) -- please note that these hotlines are NOT free of charge if you call them from abroad!
