Plus valia works on the same basis as capital gains tax, but isn't - you are still liable to CGT on top. Though that's not until you come to sell the apartment.

It sounds like your soliciter either got the amount of plus valia wrong, or more probably didn't bother to pay it at all - you need to get onto him and find out. If you consider he was incompetent or dishonest you should make a complaint to the local Colegio de Abogados.