Penalty for delay upto actual possession vs Offer of possession

Sir, I have been reading your kind advices on different issues. I have a small query regarding current view of RERA regarding penalty payment on delay in possession. I have been booked a flat in Mahagun Mywoods (developer). I had paid all the installments as per schedule under CLP. Developer have also received Partial Occupancy Certificate, and then issued offer of possession(01.03.2018) to me thereafter. The project was to be completed by 30.07.2017 but got delayed. As per agreement Mahagun paid delayed penalty upto the date of issue of offer of possession. ie. upto 30.02.2018. However,even after offer of possession the work in unit remained incomplete due to shortcomings in civil works and hence I could not take possession in my flat. I took possession of flat now in Aug,2018 after repair works but Registry is yet pending as I am yet to received communication from Mahagun for that. I have requested builder for Delay Penalty for period in handing over possession from 01.03.2018 till date of actual (deemed) possession but they are refusing on the pretext that I should have completed possession & registration formalities earlier while in really I have been following up with them to complete the flat....Please Advice...whether my claim for delay penalty valid and building liable as agreement till date of handing over possession?