Taking loans from banks or elsewhere under the interest system is a form of jaahili riba which was abolished by Islam, and declared to be extremely haraam, and concerning which a warning is issued that is not issued with regard to any other sin. Buying a house is not regarded as a necessity that makes riba permissible, because necessity refers to something the loss of which will cause death or almost cause death. The need for accommodation may be met by renting, or by staying in a small house, until Allaah makes things easier.
It would have been better for you to put up with the wrongdoing of the increase of the price of the apartment, instead of resorting to dealing in riba. Hence you have to repent to Allaah from this grave sin, and resolve not to do it again.
See also question no. 39829.
Remember that the more you hasten to pay off this loan, the better it will be, so that you can get rid of the effects of riba and its bad consequences, but you do not have to do that. Based on that, you do not have to sell your car in order to pay off part of the debt.
And Allaah knows best.