This is a rather unusual request. Is this to set up online banking? Usually confirmation of a mobile number would be via SMS or a call to that number. Why does the bank need to see a document?

This is to change my banking number to my German one. Since this is in Greece, they have a lot of security measurements and they only accept Greek/English. 
Sadly it’s the way it works here and I need to change my number in order to use mobile banking. They do not accept anything else. 

Hi @Taco thanks for writting us here in the community 
Unfortunately the customer information for the new contracts are only in german available.
When you are looking for english informations, we have an article for you.

kindly regards
Michael