I work in insurance but not motor. If it's not in the policy wording then you should have the right to complain. Have a look at the cancellation clause, how much time you have to give, what situations you're not able to cancel etc.
In other kinds of insurance e.g. marine the full premium is due if the subject of the insurance is lost/written off, but I don't know if this applies to motor.
If the accident was not your fault the insurance company ought to be able to subrogate against the guilty party in which case you shouldn't be penalised.
Sorry I can't give you proper advice as I haven't read your policy terms and conditions and don't have any experience of motor insurance!