billed 499 instead of 199 and don\'t return the money

I bought 2 pairs of slippers from reliance foot ware one was Frisbee rupees 179 with 50% off and other one paveps rupees sticker with 599 and discount tag with rupees 420. The billed Frisbee correctly but Paveps as 700 and after discount 500 , I had a confusion but I was not able to check my bill as they don\'t hand over the bill till I got out of the store. After going home I found out that I pay 80rupees extra.. I went to the store asked the sales person how much is the Paveps slippers after discount he said it is rupees 199 after discount. I showed the price tag the bill and the slippers also.. They first said that they don\'t have any product of rupees 420, they I said is it your stores tag, they asked me to go and get the other pair so that they can check( such manner less staff) when I went upstairs and asked the sales person he said that it was rupees 199 . when I went to the billing counter showed them the same . They said that the product is billed and they can\'t do anynthing for that, it is their mistake but can\'t do anything.. So for their mistake I have to pay rupees 499 for rupees 199 slippers. They took the bill and price tags from me and I had to leave the store .

some one suggest me what to do. I have to pay for their billing mistakes.