If Construct crashes, make sure that you have updated your graphic card drivers.
As DuckfaceNinja said, Scirra is a two men team (not a mutlinational with billions of employees) who's probably taking some well deserved time out during those end of year holidays. Give them a few days and they'll come back right at you.
Also you're complaining over the fact that the version you bought requires Steam to run, than in this case you shouldn't have bought the Steam version but bought it directly from Scirra's website.
For this it's nothing but your own fault as there are lots of threads on this very forum (an example in this very first page) that states the pros and cons of buying on steam.
I'm sorry you're having a bad experience but please give it a bit of time to get solved. It's Christmas/holidays for everybody.
Just out of curiosity, when did you buy your version, when did you send Scirra an email and what are your computer's specs and OS ?