Phone the Insurers to explain the situation to them and see what you can do. Can you suspend the policy to stop the cancellation for a short period.
With these trade policies, if they are cancelled mid term you have to pay the full years premium, which may include various costs.
Depending on how the phone call goes, if you need to, register a complaint about not being made aware of the cancellation terms of the policy when it was bought. If you can make the case that they did not provide you with the information you needed to know about, they might just cancel, without charging you the full year and just cancel with a time on risk up to cancellation date. Use the complaints procedure to your advantage. If you go to the FOS, it will cost them a £500 case fee and you nothing, so the Insurers try to reach a compromise.