As already mentioned, the best option is via Paysafecard. Paysafecard, however, requires a completely registered business. This means: deposit tax number and complete address, as well as go through ID procedures. However, it is up to you to decide whether you want to support other mobile phone providers. A simple solution would be e.g. the choice of your own mobile network. Let your customers pay you with credit codes for your mobile phone connection.