Cheque with someone with a written amount and they are threatening me.

Dear Lawers, I was previously working with a car owner, as a driver for Uber. Later he/she showed their willingness to sell the car to me. I agreed and on mutual words, i agreed to pay Rs.1,20,000/-. We both where staying in same building only. They handed over one car key to me, i gave them two cheques of Rs.60,000 each, cheques where in my wife's name. The car loan was continuing in their private car loan with karnataka bank. I used the car for one month time (Around 300kms), and i returned it back to them, coz i got a job and i was not able to drive the car and earn from it, also they where not ready to give an agrement in my name. By the time i paid them Rs.20,000/-. Since they where not accepting to write an agrement, i refused to continue the deal. And they continuosly started abusing me asking for money each and everyday, when i am back from office. When it became crucial only, i returned the car. Now they are threatening me that i have to pay them Rs.75000/- more.