[wdfifteen]

The airline only gave you the voucher to make a not-so-ticked off customer. They had no obligation to make you whole. So if you are pleased with the treatment they gave you, they got their money’s worth.
The insurance company, on the other hand, appeared to make little effort to make you a happy customer. I suppose at some level you owe them the voucher, but what are they going to do with it?
I had to use travel insurance twice and both times I had to submit a doctor’s report of sudden illness in order to get paid. That’s not unreasonable.