If the cancellation was in Hotels.com’s system, then one of two things might have happened. Either Hotels.com failed to notify you of the cancellation, or the email never made it to you because of your spam filter.
It’s difficult to know whose fault this was without conducting some digital forensics analysis. And in the end, it probably doesn’t matter. When Hotels.com learned that you were in Paris sans hotel, it should have tried to help you. Leaving you to fend for yourself isn’t my idea of good customer service.
You might have avoided this by calling Hotels.com or logging on to the site and verifying your reservation. If the reservation had been canceled, then it wouldn’t have shown up, and the situation could have been addressed before your flight. Also, consider “whitelisting“ emails from Hotels.com, so they’ll always get through.
The thing is, when you’re stuck in the hotel lobby, all you can do is call your online travel agency to fix a problem like this.
If it can’t, you’re on your own.
I contacted Hotels.com on your behalf. It refunded the $360 difference between your new hotel and your previous reservation.