You should see Paypal, Paysafecard, MINT, Mobiamo and a bunch of other options for Germany. You only see Mobiamo mobile?? Are you trying to donate from inside the game (TOPUP button of mall) or on the website page?
Are you using any IP or location hiding service to browse the internet, or a VPN or something? The page needs to know your real location or at least country to show the correct payment options.