Jufus, try calling the HT's secretary to ask for the meeting to be scheduled. If nothing else, he won't like you bothering his secretary.
If you are going to make a formal complaint, then keep a diary of the time and date and roughly what was said.
I suspect, however, that if what you want is for the HT to fix the most basic failings in his school, such as those you've described, then you will be disappointed. S/He obviously can't keep his staff and he knows this. S/He probably has a very good handle on why they leave, and why its difficult to recruit reasonable replacements, but s/he isn't up to doing anything about it, else they would be doing it already.
Even if the most dynamic, effective HT came in this afternoon, would they be able to turn things around for your DD and the rest of the year 11s?