Ticket Stuck

I’m not sure if anyone here can help but I’m not getting a response from their customer support. I bought a round trip ticket from London to Bruges via the website. Later that same day I decided I wanted to stay later so I used the app to change to a later train on the same day. I never got an email confirming the change and now when I try to access my ticket I get a notice that says “sorry but we cannot retrieve your journey details. We’re still waiting for this booking to be completed. Please contact your original point of sale.” I’m traveling next week and not sure what to do.