Do I Really Owe This?

I live in MO. My wife divorced me in Nov '06 after having 3 affairs on me. At that time, we thought that our house was worth about $180,000. We owed about $140,000 on the home. Just two weeks before my wife left me, we took out a 2nd mortgage on the house in the amount of $20,000, making our total mortgages about $160,000. It was meant to pay off some credit cards (around $6000) and finance my business. The money was put into our joint savings account. When she left, she took almost ALL of that money, totaling close to $10,000. When we took out the 2nd on the house, I had no idea she was planning on leaving. But when we divorced, based on what we thought the house was worth, I agreed to pay her what we thought was her remaining half of the equity ($10,000) within two years of our divorce. That deadline is coming up in Nov '08.

Last summer, I tried to refinance the house to combine the 1st & 2nd mortgages and had it appraised. The appraisal came in at $164,000. I didn't agree with it and asked for it to be done again- this time it came in at $162,000! Obviously, I was not able to refinance the house because there was no equity left, but more importantly, I learned the house wasn't worth anything near what we thought it was. In my view, my ex already took her share of the "real equity" when she took the money out of savings from the 2nd mortgage. I recently lost the house in foreclosure, which complicates matters further. The divorce decree states that the money is due immediately if I sell the house or default on the loan.

My question is this: Can my divorce settlement be modified, showing that we were incorrect with our assumption of the house's value and show that she already took her share of the equity in the home by taking funds from the 2nd mortgage, thus alleviating me from paying her an additional $10K, as I originally agreed to, using incorrect assumptions? Someone please help!