The insur co made a "mistake" and now demand money

I left work (New Jersey) in November 2002 and was on vacation pay into January 2003. When my paid time off ran out I applied and rec'd short term disability. During the summer of 2003 I applied and rec'd long term disability through my policy at work. It was required that I apply to SSD, which I did and was recently approved. The insur co withdrew the retroactive $25,000 from my acct. After doing that they reviewed my acct and state that they made an error 3 yrs ago and I owe them approx $15,000. In 2002 I had a policy which covered 50% of my salary, in 2003 I was covered for 60% and since I applied in 2003 that was what they based my compensation on. Now they say it should have been based on the 2002 policy and they want the difference. This "little" error of theirs may cost me my house. Do I have any rights. Any advice or help would be appreciated.

Hire an attorney. We can't litigate from this forum