actually if you wanna have fun with this.......................SUE THE **** OUT OF THEM!!!!!!!!!!!!
if as a part of your employment/salary negotiations your schedule was fixed as not including weekends that can not be used as grounds for dismissing you. even though you woudl have been with in the traditional 90day probationary period, they can't hold it against you.
also, if your position had a set number of hours per week you can not be required to work extra hours unless you have a contract that specifically states that you can be held accountable for overtime/extra time with proper notice.
i believe it would be fair to hold them accountable for however much you would have earned until you reached 65 including annual salary increases based on whatever pay scale system they use and some punitive damages never hurt either