How to file a report for discrimination?

Evidence 1. Job advert as advertised on newspaper or online
2. Your Curriculum Vitae, certificates and copies of correspondence exchanged with the employer or provider of a service
3. Recording of the job interview, remember that you have to advise the person that you are recording them according to the Data Protection laws, if you are keeping personal information about them. If you do not quote that you are citing criminal law, as this is legitimate purpose, and, that you are a private investigator.
See the information at https://socialdialogue.gov.mt/en/NCPE/Pages/NCPE_Home.aspx, you need to fill in a complaint form and an arbitrage process will be initiated. You may be required to witness as well. Different countries have different validation and criteria and some of them are not so clear in their validation requirements, it is useful to ask questions where you feel your complaint has not been handled as you wish it was. A book titled The Face of Discrimination available on Google Books details the qualitative data that need to be available, and, these include details of what happened (facts), an explanation of what happened (response), witness statements - preferably signed and initialized so they are more credible (witness), information on the perpetrators and the contact details (who), ideally a legal endorsement of the facts (legal attorney), and I would add legal references as the claim might be presented in a manner that indicates which laws and policies were breached by the facts or events reported. If you are no longer in a position to write it up, have a lawyer write it up for you, preferably a rights lawyer.