Leasing in UAE

I signed a 48-month lease for a brand new car. However, after a year, I was not able to pay for the lease for two months.

I returned the vehicle to them during the two months. But I found out that they have rented out the vehicle to others. And they are still asking me for the whole amount of the lease during the 2 months.

Is it fair? To ask for the full lease payment while also renting it out to others?