I see it's too late now, but just in case it's helpful for anyone in future, I thought I'd mention it's worth trying the train operator's social media.
DS left a bag on a Southern Train. The lost property number only went to a series of recordings, no person, and the form on the website for lost property said we should expect to wait a few days for an answer.
We checked in lost property at our destination a couple of hours later, while on our return journey, and the staff at the station suggested we try Twitter.
So, we DMed the Twitter account for Southern and got a really helpful person who enquired which train we had been on. Within 10 minutes they'd established the bag had been found, and where it was - sitting in lost property - luckily, at our original station, so we managed to retrieve it before going home.
It was good old fashioned customer service, communicating with a real human, like you used to get on a phone call - only via Twitter DM.
I have no idea whether other train companies have the same, but certainly worth trying if you're not getting anywhere on the phone. I was impressed!