I also work between christmas and new year, I am also on call for christmas, boxing and new years day (carpet cleaning). Last year I had to go out on boxing day to remove red wine from a very expensive white carpet.
If you really dislike anyone working at christmas especially if you have to run them off, I take it you do not go to the shops, the pub, the garage.
You also will not be watching the tv, in fact onless you have independent means of power, you should be sitting in the dark and cold because someone has to work at christmas to provide you with these and other services we all take for granted.
I cannot see why a window cleaner cannot work between the holidays.
and finally if anyone tried to run me off, they would find that the new year brings dirty windows unless they start to clean them themselves, because I will not be coming back.