Supertech — flat is not ready even after 6 months of ndc and 9 months since settlement of all dues

I have made full payment for my flat in capetown on 17 june 2017. Post that i have received no dues certificate on 16 september 2017. Ever since i have been visiting the site to get update on the status of work completion of the flat or talk on phone with the concerned officials who are handling the same. Every single time i get the same response that there is material shortage at the site due to which handover is delayed. Need to understand why there is so much delay and i would like to have the interest cost reimbursed to me at the same rate of interest as they have charged from me for delayed payments.