To be honest, there's nothing much you can do because it is your responsibility to check the policy documents to make sure the details listed are correct. If you haven't notified the insurer that the IN10 conviction was missing on the policy, then they would assume you didn't have one and that forms the basis of the policy contract and is reflected in a lower premium. All car insurance companies send out the car insurance policy through the post even for online only companies (accessible through websites only) and therefore you would be blamed even if the website was faulty.
Even if you can prove the website has a problem, you would still be liable for not checking the paper policy documents. So unfortunately, your insurance would still be considered as invalid.
