about signing noc

i ve agreed to buy a flat in 2019 n we gave 5lakh in advance after that bank found a problem in the paper so we decided not to buy the flat and it was agreed through our conversation that he will refund the money as soon as the flat sold but afterwards he kept it for himself not sell it.however later i learnt except that all the flats were sold but he told me that he will give me back money n for that he prepared a noc but mentioned in the clause that i ve not taken it for my own personal reasons n did not put any time duration of returning it.so what should I do sign it as it is on noc or ask him something to put on
the clause for my protection.please tell .