Agreement to give remaining payment but not done yet

I sold out my property. And my property papers are with the bank. Buyer is asking to give in written that he will collect the papers and New sale deed is also done in his favour. But I have still 30 % of the total payment is pending. He will pay me my balance on receiving documents from the bank. Possession of the property is with me only. And New/Old sale deed papers are with him. He has also given one security cheque of the same balance amount and agreement on 100 rs stamp paper with witness to pay my balance money in cash and then only will take the possession. How far my balance payment is not done.