It can sometimes take a while to pop up. What I would do is contact your insurer again, raise a complaint, advise you are also raising a complaint with the Financial Ombudsman and you want them to place in writing that you are covered and the policy is on MID (request to speak to a manager and insist the email confirmation). Print off your certificate of insurance and carry it in your car for the time being, just in case the police pull you over.