Advance payment

We struck a deal to sell our house for 50lacs . The party paid us 2 lacs as advance , and we agreed aeound 6 months for full settlement . They paid around 12 lacs more in subsequent months . But in the end of the 6 month period , they suddenly said that they dont want to buy the house and need full refund of 12lacs + 2 lacs . We paid them 10 lacs and said 2 lacs will be refunded once the house is sold , due to there persistent torture , we somwhow managed to return back 1.25 lacs also ! and remaining to be paid once the house is sold ! . But now again they are calling and threating FIR if we dont pay back 75k within 24 hours . They dont have any documents but still its a huge torture as we are in Kerala now and our house in issue is in MP . So any FIR or Case will be trouble for us .The house is also Unsold till date just because we wasted more than a year hoping they would buy just in the end Breaking the Agreement and causing Huge Mental , and Physical torture . What should we do now ? .Thanks