Insurance companies will do whatever they can to deny a claim. They are in the business of taking in premiums, making investments and finding new and inventive ways to deny claims.
Cheers
Not necessarily true, especially for the established companies.
I had a long conversation with an insurance adjuster and it was a real eye opener how people try to rip off the insurance companies by making false claims. He had become an expert in estimating how many cd's a person really had from a pile of melted plastic ("No sir, you had 50-75 cd's, not 200"). He explained that the insurance companies are plagued by 10-20% of abusers and fraudsters that drive up costs for the other 80%. When the 80% make a claim, they're perfectly happy to process it and move on. Competition amongst insurance companies is fierce and having a (legitimate) pissed off customer isn't good for business. The tricky part is separating the wheat from the chaff and sometimes they make mistakes.
That said, asking for a GST number seems a bit weird. My guess is that something about the OP made them suspicious and caused them to probe further. And as one by one the explanations couldn't be provided (receipt is faded, store is closed, etc.), it didn't do anything to alleviate their concerns.
Personally, I'm okay with insurance companies doing their due diligence. Keeps insurance rates down (or at least lower than they'd otherwise be) for the rest of us.
If you go through life with the attitude that everyone's out to screw you, well, don't be surprised when that's exactly what you get. Shit it = Shit out.