Hi Missh
So sorry to hear what Thomas Cook have done! We are booked to stay at the Mythos in September so I hope that there is nothing seriously wrong!
Thomas Cook also go to the Vicky Apartments and the Kapentanios in San Steph. I would try to see if there are rooms available at one of these and asked TC to put you there.
We have just returned from SS and the resort was alot quieter than usual so there may be a chance that either of these two may have empty apartments.
Just checked the TC website and the Mythos is still being sold - to fly out on Monday, but only for a 7 night stay - chances are TC have overbooked your accommodation!
If you have no joy with the above, I would suggest that you request Arilas instead - a MUCH nicer resort than Sidari. We were told while in SS that the Tour Operators are struggling to fill Sidari and now push the accommodation here before other resorts.
Good luck, and whatever happens I hope you have a lovely holiday.