Last Saturday there were major construction works on the rail network in London. Euston station was closed.
I had to travel from Glasgow to the south of London. I had originally booked a return ticket Euston - Glasgow - Euston via Virgin's website, well in advance. When I was made aware of the engineering works in the middle of July (which resulted in my train being cancelled), I called Virgin to re-book, and they offered me an alternative to go from Glasgow via Milton Keynes and Clapham Junction. That sounded reasonable. Their price would have been higher than my original ticket though, and I saw the exact same connection on Trainline for half the price. When I told them they said they can only offer tickets for the same price or higher when re-booking, and offered to refund the return ticket instead so I could book myself, which I did. This question is about that new one-way ticket from Glasgow Central to Wimbledon via Milton Keynes. The pre-story is just included for a frame of reference.
Fast-forward to Saturday; I went on the Virgin train to Milton Keynes, and the train via Clapham Junction that Trainline said I should take did not exist. It wasn't cancelled, it didn't not show up. It simply wasn't scheduled. The only thing that was there was a train to Hemel Hempstead operated by London Northwestern Railway, and then a replacement bus operated by them to Stanmore Underground station, where we could take the Jubilee line into London.
This added a good two extra hours to my journey. It was obvious there would be engineering works, and that's why I tried to plan ahead. However that didn't work out. I would now like to claim compensation because I was late, but I don't understand from whom.
I believe it's not Southern's1 fault for not showing up to take me to Clapham Junction. That train was not late, or cancelled. It was not advertised on the board in the station, it didn't show in the live departures at National Rail's website when I checked while I was in Milton Keynes. It simply did not exist. I believe I should not have been sold that ticket.
It's an Advance Single ticket that has a seat reservation for the Virgin leg, and no information about what trains exactly to take after that. I bought it on the 20th of July. Here are the trains that the confirmation email showed.
The Trainline app still showed the trains that it originally claimed I should take (via Clapham Junction) when I was traveling.
Clearly there was something wrong with the ticket booking system in the backend, or both Virgin and Trainline wouldn't have offered me the same route for a train that could not run.
Chatting to Trainline yielded hardly any new information. They didn't fully understand the problem and say I should claim from Southern. They also claimed Southern altered the timetable, but couldn't back that up.
Whom do I claim my compensation from, and how?
1) The direct trains between Milton Keynes and Clapham Junction (and thence to East Croydon) are part of the Southern Railway franchise. They should have operated the train that I bought a ticket for.