I was caught up in this at Totnes, so perhaps I can give you some information on what actually happened.
I'd taken a trip on the South Devon Railway and I walked through the station on my way into the town at about 4.30pm to have something to eat. There was a Cross Country HST in the west bound platform waiting for something, but I didn't really think very much about it. When I got onto the main road, there was a large queue at a northbound bus stop nearby, but again although it looked odd, I didn't think too much.
When I got back to the station to get the 18.53 or the 19.14 trains to South Wales (the former via Bristol Parkway, the latter direct), I found that they'd both been cancelled - and the 20.15 had also been cancelled as well. There were a few people on the platform going east, so we contacted the help point. They weren't very helpful at all, and didn't seem to understand that I wanted to go home and didn't want a night in Totnes (not that there's anything wrong with that).
I then spotted a member of the GWR staff and asked him what was happening. The chap was almost at his wits' end, as he'd been trying to contact coach firms and taxi firms with no success since around 4.00pm. There simply weren't any of the former, and all of the latter were either fully booked or simply not answering, probably because they were fully booked. He could only say that I should try the taxi firms myself as I assume he was going to continue to do. He had a big problem, though, in that if he was in the office on the phone, he couldn't be on the platforms answering questions, so he was on a loser from the start. He did have some help from some Cross Country staff, who were presumably stranded on the station, but again there wasn't much that they could do.
I rang about four taxi firms; two didn't reply, one was in Plymouth and the other was in (I think) Exeter, so couldn't help. There were taxis arriving to collect pre-booked fares, so I then decided to ask the drivers for help. One of them couldn't help as all their drivers were busy, but I was fortunate to talk to one who was supposing to pick up a fare but wasn't sure whether they'd be wanting the taxi. It turned out they didn't, so I was able to book them and get to Exeter.
The problem with taxis in Totnes is whilst there's a large board with around a dozen firms on it, my driver said that they're all small firms with few drivers, and quite a few of them had ceased operating because of Covid, so they weren't available any more. It's also not possible to hail a cab at the station if they don't have a licence to take fares off the rank - I had to make a booking by phone for my taxi whilst standing next to the car.
Anyway, I got to Exeter, where the situation looked chaotic, although I will say that there were plenty of staff there dealing with it. They'd obviously decided to turn the incoming trains around there rather than letting them go any further, which made sense. Whilst I was waiting for my train, a coach from one of the local firms arrived, but where it was going (presumably to the west) arrived, so the position seemed to be getting better. In the hour that I was at Exeter, the numbers went down quite a lot, although there were still a fair number waiting when I left at just before 8.00pm.
I can't really complain about the actions of the staff at Totnes and Exeter St Davids. They did their best, especially the poor chap at Totnes, who really couldn't do anything to help because he couldn't contact anyone to move people on. The only exception was the helpline, which was very poor - they didn't seem to understand the problem and obviously weren't local, and only wanted to pass the problem onto someone else - again at the end of a phone, and who wouldn't / couldn't answer my call.
So there we go ... your report from "the main on the spot", and I hope that this has helped you understand the situation.