Housing society promoter charging both VAT and Service Tax

I purchased a flat in SCC Saphhire project in Raj Nagar Ext, in ghaziabad, uttar pradesh. All the installments, along with service tax, were duly paid from may 2012 to march 2014. As per agreement, the project was to be completed by march 2015, although is still incomplete till date. Recently I received a final demand letter from the builder asking me to deposit VAT @Rs.22/sq. ft. on the entire cost of apartment. He has also demanded GST on the VAT. Why should I pay VAT when I had already paid Service Tax on the entire amount? Will I be taxed thrice on the same amount? First-service tax, second-VAT, third-GST on VAT.
The VAT did not exist during the tenure of payment. The builder delayed the project. So if any VAT is applicable later during construction, then it has to be borne by the builder, not the buyer.

Kalpana Gupta
Ghaziabad 201001, Uttar Pradesh
Email: sxxxxxxxxxxx6@gmail.com