To who should I pay the annual fee for the domain? 

The annual fee for your domain is charged the first time through the creation of GoMINIsite and DIR.dk.
Hereafter you will be subsequently charged annually by DK hostmaster A/S.

DK-hostmaster have the following address:
DK hostmaster A / S
Kalvebod Brygge 43
1560 Copenhagen V
Denmark
www.dk-hostmaster.dk