Hmm... I wonder if there's a common postcode lookup software used in Germany that's to blame for this?
I recently moved house and had to update my details on Spreadshirt's [also a German co.] website. As with you, their site refused to accept my postcode was a valid postcode and wouldn't let me change my ddress. This also had the side-effect of locking my account.
After I emailed Spreadshirt about it, I had to go through the ridiculous palaver of them sending me a snail mail letter from Germany to my address in UK, containing a code which I had to then email back to them. At which point, they finally accepted that I [as the person who actually lives in the house!] might actually know my own postcode better than some database lookup software they were using in Germany.
I recently moved house and had to update my details on Spreadshirt's [also a German co.] website. As with you, their site refused to accept my postcode was a valid postcode and wouldn't let me change my ddress. This also had the side-effect of locking my account.
After I emailed Spreadshirt about it, I had to go through the ridiculous palaver of them sending me a snail mail letter from Germany to my address in UK, containing a code which I had to then email back to them. At which point, they finally accepted that I [as the person who actually lives in the house!] might actually know my own postcode better than some database lookup software they were using in Germany.
Teutonic efficiency at its best!