Had a similar issue with British Gas.
Our smart meter wasn’t programmed to handle on/off peak tariffs. So we were being ‘charged’ the same day-rate through the night when charging our EV.
Flagged it up after a few months. British Gas refunded what we’d paid according to THEIR numbers showing at their end, in credit.
Our Smart Meter took about 7-10 days to ‘update’ from there. Now displays the correct tariff 12am-5am.
I’d recommend people have a quick one off check to make sure they’re on the correct tariff, according to their smart meter during ‘off-peak’ hours. Though these devices seems tricky to navigate for many..