Assignation of positions on GEO

Hi, group
Out of curiosity, anybody could tell me who is responsible of assigning
positions on the Geo stationary orbit to the different satellites (mainly
commsats but also meteo, military etc). Does the owner of the satellite
has to pay a fee for the assignment? When the satellite is no longer
working and is turned off, can it be moved somewhere else and its possition
be reassigned? Or just stays there forever taking valuable space?

Thanks
Rafael Clemente