A list of trust service providers is available. Please consider that, although it may result practical to request the verification from a provider in the same country where the organisation is established, this is a free and open market, thus, in principle, your organisation may look for best conditions abroad.
Disclaimer: Please note that the European Commission cannot provide a legally binding interpretation of the EU legislation, as this is the sole competence of the European Court of Justice. Any remarks from the European Commission services are without prejudice to the position the Commission might take should related cases arise in a procedure before the Court of Justice.