What exactly do you mean by "Interrail two pass numbers”? Do you have 5 mobile passes but only received 2 pass cover numbers? In that case, that is not necessarily a problem. The pass cover numbers are not printed on the reservation, except for Italian trains booked via Interrail (but that can also be done via ÖBB without any pass cover number).

Or do do mean you ordered 2 passes and have 3 children that travel for free? In that case, did you indicate in your order that you also needed 3 children? And in your message to customer support, did you indicate when you need the passes to travel?

Also, this second case does not mean you can't book reservations, since you can often also book these elsewhere. If you indicate which trains you'd like to book, then people can suggest other ways to do that. Please indicate per train: origin, destination, date, departure time.

I mean we have 2 Interrail Order Numbers, so we have a group of 3 (1 adult and 2 children) in one order number) and a group of 2 (1 adult and 1 child) in another order number.  

So I want to book the Eurostar from Paris to London -  Thursday 7 July Departure 4.13PM    

Thank you,

Jenny

You should be able to book via the Interrail website (booking fee 2€ per person and train). Do look at this page to be able to book together. Customer support won't answer soon since the information is on the website.

Or book via Belgian Railways if you have pass cover numbers (booking fee 4€ per order so that's cheaper). Alternatively, you can call SNCF (press #85 for English, no booking fee but phone costs).