Zivame — Charging extra for the discounted product

Address:

Camp , pune

I bought a bra from the zivame store at camp, pune whose MRP was 799/-. The store manager asked to chose a pack of two panties saying that it was free with bra and charged me 839/- for both. On asking what the extra 39/- were for, they told its GST . when the MRP already included all the taxes why did she take 39/- more?