I think they are checking accounting to see if there is another 1.9 billion missing 😀
I don't think that they are looking at their clients, everybody under the sun uses wirecard cards .. When transferwise support told me they were issuing their own cards I was shocked, because I was used to the fact that everybody just uses wirecard, it was automatic in my mind ..
EDIT : wait you just said "all customers of clients of Wirecard" lol, so obviously you were joking 😀 nevermind !