Outstanding finance on a car I bought

[Jackstan]

Hi, help needed please. We swapped our car for another and a few weeks later have received a letter from a finance company saying it had outstanding finance. We called the company and they say they are going to come and repossess the car. We had no idea there was finance on it and for the first time ever, had not done an HPI check
the person we swapped with had bought it from the person owing the finance company so we are assuming he got a similar letter and hastily decided to sell/swap.
We obviously can’t afford to lose the car. Should we have good title to the car and how should we proceed?
Thanks