Case C-375/11: Judgment of the Court (Fourth Chamber) of 21 March 2013 (request for a preliminary ruling from the Cour constitutionnelle — Belgium) — Belgacom SA, Mobistar SA, KPN Group Belgium SA v Belgian State (Telecommunication services — Directive 2002/20/EC — Articles 3 and 12 to 14 — Rights to use radio frequencies — Fees for rights to use radio frequencies — One-off fees for grant and renewal of rights to use radio frequencies — Method of calculation — Alteration of existing rights)