Swift command module not working on new 'van

When PSU switched on, a battery overcharge alarm is shown on command screen - 20.5 volts, which shuts down the command system. My battery app shows 13.2 volts, which is normal and, I'm sure, accurate. The shut-down means that the 12V system doesn't function. So no heating, water pump, TV antenna booster, hob ignition or awning light. On the command module only the 2 advanced settings screens are available, but the main control screen flashes on for a split second and the screen turns off automatically. The top line of the advanced settings screen shows a 100% battery charge, but again my battery app shows a 66% charge level which doesn't increase when the 'van charger is switched on; so it looks like  the 'van charger has stopped charging the battery although the charger fuse is intact and the green charger button is illuminated. The new 'van was delivered in November and everything was working until a couple of days ago. All 240 sockets work inc. fridge and microwave - all on MCB1. Road lights all flash as normal when alarm is set and unset. Spoke to Sargent who seem nonplussed and suggested either charger or ammeter problem in PSU. Caravan dealer is in full lockdown; so understandably no help available there. Does anyone have any suggestions as to fault resolution? Thanks JW