Refund of vat from builder

I had booked a flat in 2014 April in Bangalore by paying booking amount along with its VAT and service tax. After 6 months builder sent me sale and construction agreement and since it was not agreeable for me I decided to cancel the flat without signing the agreement. Builder has refunded the principal amount, but not refunding VAT and ST. My concern is why have they paid tax without executing agreement with me? I have got nothing in return but ended up paying VAT and ST for no reason. Please help me to understand on how can I get a refund on VAT and ST?