1. On which website did you book?
2. If you you booked on interrail.eu, is there anything about this booking in your reservations overview?
3. For which train was that (route, departure time)?

I booked via the website of interrail itself. There is nothing in the reservations overview.

These are the reservations I made on 25th of September

1017h Bruxelles to Valence

1514h Valence to Barcelona

2015h Barcelona to Valencia

Reservation on 6th of October

0910h Barcelona to Paris Gare De Lyon

1725h Paris Nord to Rotterdam Centraal

If there's nothing in the reservations overview, then the booking didn't work. You'll get your money back eventually, or you can request a full refund via customer service:

https://eurail.zendesk.com/hc/en-001/requests/new

That also means you'll need to book again:

• 1017h Bruxelles to Valence: via SNCF, NS or NMBS (ticket office or by phone).
• 1514h Valence to Barcelona: SNCF by phone. Press #85 for English; reservation will be sent via email. Other options in this post.
• 2015h Barcelona to Valencia: not possible online. See this post for the options.
• 0910h Barcelona to Paris Gare De Lyon: see Valence-Barcelona above.
• 1725h Paris Nord to Rotterdam Centraal: online via NMBS (booking fee 4€ per order), or via SNCF, NS or NMBS (ticket office or by phone).