La Pino'z Pizza — incorrect billing - airoli centre

Airoli centre cheated on takeaway Bill. Friday is Buy1 Get1. Orderd a medium of Rs455 n opted same pizza free. Ordered another medium of Rs645 n opted same free. Bill should have been 1100{455+645}+ 27.5{SGST}+ 27.5{CGST}= Rs1155 but was actually charged Rs 1355. The sales person after a lot of argument asks me to complain with anyone but nothing will happen. What's the value of a customer who pays his hard earned money, nothing? Rs 200 is not easy to earn unless you have a great job.