OK so you book your flight 3 months in advance and they sell your seat to the next guy and you can't board.
Update: the contact with customer service was quite good and I was put on a flight to Amsterdam a few hours after my flight to Eindhoven left. Got a financial compensation as well.
Lesson here is to always check in in time.
The flights were OK no complaints there. I will upgrade my score from 1 to 4 stars and will be using them again.