Car was either repossed or stolen. Tried to check with comoany and they had sold out to another company. How can I prove I no longer have the vehicle?

Repossed or stolen?
If you have a lien on the car, it's yours until that obligation is met. If it was repo-ed you will need to contact the lien holder to be certain the debt has been met.
Insurance could help if it was stolen and you filled a report.

Just because you don't have the vehicle doesn't relieve you of the responsibilies.

So how can you not know if it was repossessed or stolen? You woke up one day and the car wasn't there and you just thought... "Oh well..." ? You didn't report it or try to find out what happened?

Anyway, as the Captain already said, you are still responsible for paying the debt of the car.