Once the Boletins from the tradesmen have been signed off ,the architect has prepared the book of works and the Habitation Licence issued the utility companies will put the bills in your name.The electricity company instal a fuse in your property.
Utility companies bill you for connections direct.
Until then the property is not legal. One shouldn’t have either moved in or paid final instalment. Unfortunately it is the practice to do so.
Meanwhile any services, although properly connected to utility companies, are builders supplies and builder pays the bills.
IMO this “Admin fee” is towards the utility bills the builder is supposed to pay.
Because of the corruption in some regions in Spain councils are going over the planning consents etc with a fine tooth comb .
Certainly happening in my area of Murcia where they are also visiting new builds to check build is exactly as permitted.
Consequently the paperwork is stacking up . In for a very long wait it seems.