If you cancel your car insurance within the initial cooling-off period (usually 14 days from when the policy starts), you should be provided with a refund, minus the time the policy was active and any other admin fees.
If you cancel your car insurance after the cooling-off period, any refund depends on how much time is left on the contract and any cancellation fees the provider might have, as well as any extras you have on your policy.
Remember that cancelling your insurance mid-way through the policy means you’ll lose the no-claims bonus for that year.