Excel spreadsheet disappeared and I cannot recover it

I've had this happen on Mac 365 v16.112.4. 

You open a CSV file (which opens visually and functionally as a spreadsheet). You start building on that spreadsheet, and do an hour or two of work on it, then save it. BANG - you lose everything, because it’s too dumb to save it as a spreadsheet. You should have changed the file type to XLSX or XLS before saving it. YES, there is a message which comes up in the Excel UI (not a very strong warning, like a popup "ARE YOU SURE"). Rather, there is a message somewhere on the screen that says "in saving this CSV, there might be data loss," or something to that effect. Whatever, I've only used computers since 1977, and I missed that message completely.  If you don’t see that, there is NO WAY to recover that file. NONE, no recovery file, no cloud file, no "recents" file, nothing. 

That's amateur hour, I'm sorry. The code should be smart enough to put up a real warning in the user's save path which stops you cold and explains that you need to save the spreadsheet you are working on as if it was a new spreadsheet. Forget cryptic messages. And by the way, why wasn't the file in a backup form in the cloud, or in the Library/ recovery area. Who the hell knows?

Once you guys went to subscription (rather than the pleasant old "buy the software" days), this sort of a loss should be grounds for a refund.

GK