There was not written agreement, it was a verbal agreement.
There was billing for overtime in September which was itemised. There was also billing for overtime in August that was not itemised because I did not know what they had done hence my delay in itemising it. They are now saying because the August billing was not itemised they will not accept it and expect me to pay it back. They do accept the billing for September. How do I stand legally for the billing in August?