Forfiet of emd

I entered in sale agreement for one property...I paid seller 5 lacs in cash as EMD and 2.5 through cheque as installment...later on I came to know that though property has conveyance deed from DDA but form-D of society has DDA JE's remark that further inspection date is fixed so 7 so ....and no body is entitled to go for possession of any part of society......society didn't issue possession certificate/slip also to this particular flat in delhi. I raised issue to seller but they denied and said that possession certificate is not reuired at all once conveyance deed is done by DDA. I gave seller an intermdeiate solution that he indemnify me for 20 years that if DDA ask for any liability on account of possession certificate then he will be reponsible for that. beut he denied. Last date expired but on last date agreement was extended with some condition like house will be vacated 22 days after final date of registry to which i had to agree because my 7.5 lacs were at stake. I also didn't close the issue of possession certificate. now second date also expired. Now he is threatening me not only to with-hold my EMD but also 2.5 lacs and also threatening to write to my officials and also filing a suit of Rs. 15 lacs as performance claim. Is it justified as per Law? what should be my course of action?