The way to deal with this is to stay off the technical stuff. Write to Sky and say that before their engineer called your TV was working perfectly and that after the visit it was not. Therefore you are holding them entirely responsible for the damage. You may want to point out that the fact that the engineer could not get the Sky box to work properly (which was the reason that he/she was there), whereas other boxes were working happily, may say something about his/her competence. Tell them that you give them 28 days to fix it or you will call a third party in to fix it and bill them.
BTW (DO NOT tell Sky this.) I suspect that the engineer [sic] has just screwed up your TV's settings.
T
February 2009