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Legally, you are in the right based on what he directly communicated and his failure to comply with terms.
Practically, if he pursues a labor board complaint and then consider a discrimination or retaliation case with a lawyer, the cost and legal fees will be many times your agreeing to a slight extension - even if you prevail in defending.
Kindly let me know if that is fast and clear.
Kindly rate me positively, and if I may clarify anything reply back and let me know!