Very glad you found some alternative accomodation and you're making light of the situation (losing £760 is ouchie!). You sound lovely.
When we've lost chunks of money, I've divided the amount by how many days I've been alive and told myself the mistake only actually cost me £0.01 per day (or whatever it worked out as). Helps soften the blow!
As to you not being the only one... We go to Spain roughly the same time each year. Flights and transfers booked independently, accommodation owned by our family. Always try to keep costs down as much as possible (we're not flush!). Anywaaay... Three years ago, the flight options weren't great but I pieced together a journey that involved flying out to an airport further from our accommodation then hiring a car. It was a late flight so I first checked car hire was available for the time we'd land. I went through the process five times (right up to enter card details) before booking the flights. Only then was I content it would work. Booked the flights. Great. Went immediately back to book the car hire - no car hire available at that time of night. Couldn't figure out a suitable way around it (travelling with an 18-month old) that wouldn't cost a bomb, make the travel time ridiculous or just be an enormous faff. Then decided to bury it... Right up until it was time to leave for the airport. Decided, at that point, it was better to just book a flight for two days later. What a waste!
The following year, flew into our usual airport and booked the shuttle bus (amazing service).
Last year, flew into our usual airport, went to the shuttle bus - they couldn't find us on the list. Phone wouldn't work. Driver didn't speak English. My Spanish isn't very good (try as I might!). Tiny airport, no taxis, no nearby hotels, no means of getting out of there, airport closed so no one around inside to help. Eventually found the reservation... It was for the same date but a year earlier 🤦🏼♀️ I hadn't actually booked the shuttle. Thankfully, we were able to tack on because there was room for us on the coach (though we had to pay a small additional fee each for the out of hours and late booking).
So, no, it's definitely not just you.
Have a great holiday, see if the original accommodation will allow you to bring the reservation forward and have an extended stay in Greece! Surely, that's just fate? And who wants to piss off the Greek Gods?