There are multiple place to do buy reservations, but supposing this is for reservations bought from Interrail:

1. If the issue is with the reservations sent via email, then check the Reservations overview in your account.
2. If the issue is with the reservations from the Reservations overview, then check the PDF attached to the confirmation mail.
3. If neither 1. nor 2. works, then contact customer service. Als mention the date(s) of your reservation(s), so they can prioritise correctly.
4. Always check first if you can book somewhere else, e.g. in this thread or on Seat61. If that is possible, it's often cheaper and more reliable than booking via Interrail.