If an airline cancels your flight, this isn’t something which you can claim for on travel insurance as the airlines, by law, must handle this correctly, by either offering you a different flight at no extra expense to you, or refunding you in full. If they offered you a refund and you accepted it, then, as far as the airline is concerned, that is the end of the matter.
You can read up more on the ADR website.
Do note some “low cost” airlines may refuse to book you on another airline, but they must refund you or put you on another of their own flights at no extra cost.