Raise a complaint with the Financial Ombudsman Service. I do think it is a complaint of merit, I would be advising that it was unfair for the contract to be terminated when the red alerts were over one day. It could well have been taken in for a service, a mechanic test driving and not knowing a black box is fitted. The only counter-argument to this is that your mother did know there was a box in the vehicle, was insured on the vehicle and is as such part of the contract.

I would complain to the Ombudsman that you feel the insurer is breaching "Treating Customers Fairly" TCF, as you are being penalised for your mother's behaviour. I would ask them to check with the insurer the data they have via the telematics and compare driver behaviour, and they should be able to clearly identify the difference. If the FOS find in your favour, the voidance should be removed from all databases.