Why do I owe them monies and why are they suing me more then what they paid out?

Two years ago, my boyfriend took my truck and was going to go clean it out. A lady speeding hit my truck. I did not have Insurance and the man that was driving my truck did not have a license. I called my insurance company and was told I no longer had insurance. The lady that hit my truck and I had come to agreement to walk away since she hit me and both of our vehicles was totaled out. Later, I received a call from my insurance company telling me they paid the women that hit my truck $3999 and they wanted me to paid them part of it for their mistake. Then I received a letter telling me they wanted to me pay them $3999 for the monies they had paid the lady that hit my truck. I was told they wanted $12000 then I received a summons saying they were suing me for $7999.