Benetton — gst charged above mrp

Address:

560102

I recently bought two shirts mrp: rs 2899 for each (With an offer of buy 2 at 50 percent off)

According to my knowledge my bill should have been 2899 rs. But my bill was 3246 rs which was mrp (2899) plus gst.

What i understand is:

Mrp is the final price of a product including all the taxes. If we are paying gst on the mrp, then we are charged double the tax amount that we should normally be paying.

Can you please confirm