How can I be responsible for a debt of my ex's car when it was repossessed by him?

Both vehicle were in my ex-husband’s name. After separation I kept one and he took one. The one he was driving was repoed, then he requested the vehicle I was driving to be returned to him or put in my name. I returned the vehicle to him, then he had it repoed. It the settlement it states the truck debt and all debt in his name is his debt and all debt in my name is my debt. Now he's coming after me for the other car, and said he forgot to add it to the settlement. I know in CA its community, but we already settled the debt, and it was repoed while he had it. How can I be responsible for this debt?