I believe my mortgage company has "over billed" me and my mortgage should have been fully paid approximately 14 months ago. How do I procede?

When I first applied for my mortgage, they would not approve it unless I agreed to have the payments deducted from my checking account (by them) bi-weekly (I was in the process of becoming a female divorcee). This is discrimination. I received the mortgage in the spring of 1998. The payments have been deducted bi-weekly since then as per their requirements. In addition, they have deducted and added $75.00 to each and every payment from the very first to be applied towards the principle balance. as per my request. Fast forward to today: I finally printed out an amortization schedule for my mortgage (from mtgprofessor.com) calculating in the additional principal payments. According to this schedule, my mortgage should have been paid in full after 15 bi-weekly payments in the nineteenth year (approximately 14 months ago). It is a standard, fixed rate, 30 year bi-weekly payment mortgage. I am not sure which area of practice this would fall into: Consumer law? Contracts? Discrimination?