Can you please confirm that this is separate insurance sold to you by the company which has gone out of business please?
This has the insurer pointed you to a particular clause which makes it obvious that this is not covered?
It does beg the question as to what is covered if the double glazing units are not!
Have you referred it to the Ombudsman yet or not? If so, what was said?
You really have 2 options. Assuming that there is nothing in the terms and conditions of the policy which would obviously show this was not covered, then you either get it fixed and take the insurance company to court for the cost of the repair or you make a complaint to the Financial Ombudsman that this is covered or should be covered and they are simply not paying out.
They really are your only 2 solutions.
If the original company is out of business, then they are out of the equation.
If you could please rate my service five stars (even if it’s not the answer you wanted) that would be really helpful. If you have any further questions you want to ask on this subject, I am happy to deal with those for you.