Breach of contract

I sold commercial car to SUNIL on the condition that he will pay the 36 months EMI & he will take care of care & permit fitnes etc and after completion of EMI he will be the owner, I made this agreement on affidavit. he gave that car to another person SUMIT without my permission after 2 months. when I found that then SUNIL took the responsibility of SUMIT but same contract with SUMIT & SUNIL as gurantor. after 1 year I found that they are doing something wrong with the CAR, They both refuse to return my car & start deceiving me. In Oct 2018 I filed a complaint about them. So SUNIL returned my car which were completely damaged & they were running that taxi with an private no. plate & they did not renewed permit, fitness & taxes. SUNIL apologized & write on a paper that he will pay for the damages & will pay for the taxes as well & he will return my car docs with no. plate & he canceled the affidavit but he start deceving me.I filed another complaint but now policeman is supporting him & not taking action. Sunil is not returning my car documents & the amount as per the contract.