Please note that that contracts of insurance are based on "utmost good faith" and as such an Insurer could argue that they refuse to cover on the basis that you failed to advise them that you had moved address. One of the reasons that they may state is the risk and thus premium, may have been different at for new address, thus they will not indemnify and pay for your loss.
You can challenge your own Insurers and make a complaint direct to them as to why they are refusing to indemnify you.
So can make a formal written complaint to your Insurer (you may need the help from a loss adjuster or Broker to guide you through the minefield of the insurance contract) and if you get no joy contact the Financial Ombudsman Service (FOS).
Please see the following it fully explains the process and has a template letter
The Financial Ombudsman Service will act as a Mediator, make a decision on the settlement, please see http://www.financial-ombudsman.org.uk/
You may also contact your Local CAB (Citizen Advice Bureau) office to assist you for free in this matter.
I trust this assists, If you need a CALL to discuss and more in-depth advice, then please let me know.
If not then kindly leave a Positive Rating so JustAnswer can credit me for my time.
It was my pleasure to assist you today.
The Rating can be provided by clicking the STARS on the top of your Screen