also property tax issue

I used bill pay from bank account last year but it arrived after 12/10. So I got like $250 fine. My bank record showed the check was out before 12/10, the county still denied by saying it has no post stamp on the letter. I went to bank again, the manager provided a personal letter and stated the check was mailed out before 12/10. The county still denied and asked to pay property tax  earlier next year.

Nobody knows why it has no post stamp when county received the check, which was their judgment based on. post office couldn't approve anything either. the check was mailed out on 12/5 per bank record.


what should I do? just angry.  thanks for advice!