Did you know that recently there has been a change in the Dutch privacy legislation. Even though you cannot ‘hurt’ them as much as you could in two years when the European Privacy Law goes into effect, you can scare them quite a bit.
Check out https://autoriteitpersoonsgegevens.nl/nl/zelf-doen/privacyrechten/recht-van-verzet for an example letter. You can also request all of the data they have about you and who they shared it with. At least you can push back a bit and make them do the sweating for a change!
Good luck, perhaps you can hand both letters to Maartje on your coffee date for added dramatic effect.