Purchase impossible on steam

Good evening,
You didn't put your error message...
Otherwise, has your Steam wallet been credited?

Just like you didn't include the error message, you must have made a typo when entering your Steam card. The hosting site has kindly created a ghost account (I can't think of another name) where they put your €50.
You can contact Steam administrators to retrieve your card and your amount. But good luck with that, no link is provided to reach them and their premium number is simply to be avoided (I haven't tried it, but I had this problem registering a game (The Crew) with a competitor. I was left with nothing but my tears (thankfully I bought it at Carrefour), I was able to exchange the box and the license, but for your card it seems more complicated.
Try contacting the manufacturer's site to retrieve your card
(that's all I can see) < how?: Google is your friend

Here is the error message I receive when I want to purchase a game on Steam:

Payment Information
Verification + Purchase
Your payment method does not match the store's country. The cart has been converted and the updated amount should appear on the next page. You can also check your cart here or change your payment method below.