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Unfortunately no, they are not obligated to pay you through the end of the month. When you give notice, what you are legally technically doing is immediately resigning but giving the employer the option to accept your offer of additional work. They don't have to do so. If they had immediately accepted your notice months ago, it could have been argued that this was converted to a termination, but that's not really a legal issue on these facts.
So, not allowing you to finish the month or notice period is legal.
Not paying you out the entire salary is also legal. Typically a salary can't be divided. However, one exception to that rule is the start and end of employment. The Fair Labor Standards Act expressly allows an employer to prorate payment of a salary in those instances and it is not an illegal deduction.
Finally, there is no legal requirement for a notice period for accepting a resignation early, unless you signed a contract that expressly created one.
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