Possession without Occupancy certificate

Hello Sir , I booked a flat in Noida and have received offer of possession from the builder . I requested them for occupancy certificate or to provide a specific time period by which they are expecting to get OC and to allow me to do the payment only after receipt of OC, but they are not allowing me that option . As per email communication received from the builder , they have applied for completion certificate and basis on that they are issuing possession letter to customers but are not sure by what time they would get the completion certificate / OC from the competent authority.They have also informed that It may get delayed for more than 1-2 years also.The delay in getting the completion / Occupancy certificate is probably pending because of National Green Tribunal issue going on in NCR / Noida area . Please suggest : Can I take physical possession of my flat without OC as builder has confirmed that it may take more than a year also and if I don't clear my dues and take possession of my flat then they will start charging penalty on the balance amount. They are not giving any time frame for availing OC in written or mail and asking us to take possession .