My question involves an auto loan or repossession in the State of: England, UK.

Basically me and ex broke up and he took the car that I had a finance in. I had only gotten the car 15 days prior to the breakup and he said he would change the name etc to his so I had nothing to do with it. A month later finance company tell me it's illegal for the car to be in anyone elses posession but mine so I attempt to get car back as finance is still in my name. Ex changed the owner of the car to his name. He would not return car to me so I tried to report it stolen. Police wouldnt do anything and finance company said as long as ex kept up with payments it was ok.
5 months later car is repossessed from his home address and Ive recieved a bill for 7k saying Im liable!
What do I do? Ive driven the car literally 6 times and not seen it in 5 months! No one would report it as stolen and car company knew my ex had it and wouldnt return it!