Landlord billing incorrect

I moved into an apartment last year and noticed that the invoice we got each month did not match what our lease said. I immediately contacted the management company and she confirmed that the amount they had invoiced was the correct amount. She even sent an email confirming the correct amount. A week later, still iffy, about this situation I went to the office and talked to her in person. I pointed out that the lease stated another amount, to which she again repeated that it was correct. We have now moved out are waiting on the deposit and the management company is telling us we owe $8000. I think it is unfair that we pointed out the mistake several times and they insisted it was correct. They threatened to take us to court, where do we stand from a legal perspective?