Can anyone help?

We have booked Eurostar tickets using the Interrail discount and now (long story) we need to change the date and go a week later.

Everything I’ve read says it’s 15 euros per ticket to change and that should be 60euros for the 4 of us. It even says the same on the confirmation from when I bought the tickets.

I’ve gone to exchange them online on the SNCF website I bought them from and it’s saying it’s 200 euros to exhange four tickets from London to Brussels. It would be cheaper to scrap them and start again!

I’ve checked the train and the interrail pass holder seats are still showing at 30Euros each.

Can anyone shed any light? I’m relucatant to call because that seems to cost extra?