It's pretty obvious that upper management are only really concerned about seat time (the time that you're in your office, at your computer).
There's only really two options here.
1) Find another job that requires less working hours per week (and probably pays less for that)
2) Join your co-workers and work longer hours
It might be an idea to do some other ...
In this context, date of agreed resignation is the last working day.
When you hand out notice, you are informing about the upcoming resignation, and your last working day is when you actually resign and end official relation with your employeer.
But I don't want to stay that long, how to deal with this situation?
Upper management wants everyone to work more than 44 hours per week.
Your contract requires 44 hours.
You usually work 40-42 hours
You don't want to stay longer
Clearly, this is a mismatch between what you want in your work situation and what upper management demands.
Thus, you should ...
You should really, really tell us where you are located.
The contract means that you will be unemployed for at least one month. In many locations, such a contract will be void. On the other hand, even if void, you may have to fight about it in court.
The next time you sign a contract, read it before signing, and strike out any terms like these. (I think ...
If you want to make a point in educating higher management, either approach is risky, as they probably believe in what they teach and opposing it - in their eyes - means willfully hurting the company's productivity.
Still, if you want to do something, rather make sure to have the backing of as many colleagues as possible. Then do something together, e.g. ...