From 2017 to 2019/20 my CRV was insured with Aviva.
Out of the blue I received a cheque in the post for £47.xx
It turns out that they charged me a few pounds per year more than they should have.
The total overcharge was some £28.10 - to this they added interest at 8% per annum and paid HMRC some £3.60 - the total on the cheque was for just over £47.
It's all to do with charging old customers more than new customers.
Not a fortune but 7+ gallons in the tank.