Extra VAT Charged on the Purchases

I procured shirts in two schecmes
1) buy 2 and get 2 free there is no problem as they are billing on 2 Higher MRP’s
2) 50% discount on MRP. In this case the MRP it is inclusive of VAT and at the time of billing they are charging additional 5% VAT. Now the example When MRP is Rs 100/- they are doing 50% discount value of to Rs 50 and on Rs 50 they are adding another 5% VAT the total value becomes Rs 52.5/-.
So according to me they are cheating the customers and this not fare trade practice. Pls advise on this as I need to file the consumer case also on this case. Arrow