60197 Passenger Train control problem
I thought I’d update you on the situation for anyone else in a similar position.
I got in touch with Lego via email, it took a while for them to get back due to the COVID-19 pandemic, which is totally understandable.
I received a bright breezy fun reply from someone called Ryan who said he would send me replacement battery box and remote.  Once I received these items, the train worked for about an hour and then stopped working.
After troubleshooting, I found that the connecting wire must have had a break near or inside the connector.  I contacted Lego again, and they sent me a replacement set of motorised wheels.
They asked me to send back the faulty items using a supplied label.
Absolutely awesome service from Lego.