Compensation in the case of delayed possession

I had purchased a property in January 2013 on re-sale from the original allotte whereby I was nominated as the allottee. Now as per agreement it states that if flat is not delivered within June 2014, builder will pay compensation @9%p.a. if there is no default on the part of the allottee. However, if the flat could not be delivered within Dec 31, 2014, then the contract comes to an end and the builder will refund money along with interest @ 9% p.a. from Jun 2014 till the date of repayment. Now I have been offered possession in Sept 2015 and the builder sent the bill for payment of last installment on possession. So I wrote a letter to the builder seeking compensation @ 18%p.a. (as in case of allottee defaults, 18% p.a. is charged) for the delayed period. The builder said no compensation can be given as there is a default on my part for payment of 2nd last installment for around 2 months. Also said, that no compensation can be given in case of re-sale flats and also compensation in whichever case given has been given for only 6 months i.e. from June 2014 to Dec 2014 till the date of agreement. Now, if I do not want the flat and want to get back the money, can I claim interest @18% p.a. plus compensation as the property rates have risen due to the delayed delivery? However, if I am interested to take up the possession, can I claim compensation for the delayed delivery period @ 18%p.a.? The builder though sites my delay of 2 months in the 2nd last installment and denies any interest. I agree that interest @ 18% should be provided for delayed period of delivery minus the delay of two months on my part.