Hello, and welcome. I am a licensed attorney and happy to assist.
I'm sorry to hear of this unfortunate situation, but happy to say thatyou do have recourse. The first thing to do is to go into your local bank branch and obtain your bank statements for all the years since the mortgage company claims you were first late or in arrears. You will then be able to show that each payment was timely made and that all the late charges were in error. That said, all the late charges you made an error should be credited back to your mortgage account, or your bank, if preferred.
If you don't want to handle this on your own, or if the mortgage company continues to act unreasonably after you show them the errors they made, then it would be a good idea to get an attorney on board if the amount at issue is significant enough, or if if you feel you will be threatened with foreclosure. Otherwise, with documents in hand, you can bring a small claims court action on your own. If successful, as it sounds you would be, the court will order the mortgage company record corrected and order it to pay your damages, which include overpayment with interest, cost of suit, and any incidental damages incurred on the way.
The site agreement for attorneys at JustAnswer.com doesn't allow attorneys to represent clients directly through this website, but if you decide an attorney is needed to move forward against the mortgage company, a good referral source will be your county bar association. There should be no charge for the referral and no charge for the initial consultation with the attorney to whom you are referred.