The Office of the Ombudsman for the Postal Sector is part of a network of organisations dealing with out-of-court dispute resolution. The following partners will provide you with an overview of organisations which you can consult for out-of-court dispute resolution.
The Consumer Mediation Service: https://consumerombudsman.be/en
The network of Ombudsmen: www.ombudsman.be
European Commission official website: ec.europa.eu/consumers/odr