Tax Assessment Changes

We are an association Library that uses a school ballot to levy funding. We have received a bill from the school for 2 years now that a landowner has had their taxes re-accessed back 3 years and now we owe the school money. Last year we paid it because it seemed like bad luck and there weas court documents saying the back money was owed. It seems to becoming a trend as another large land owner/company has done the same and now we owe again this year, and it's increasing. How do we continue to handle this trend and do we owe them?