Reliance Mart — Fitting error in lingerie and NO exchange policy on lingerie

Address:

Nellore, Andhra Pradesh

Today I purchased the two sets o[censored]ndergarments from Reliance Trends MART, KVR petrol bunk, Nellore. When I'm purchasing the size of the lingerie in is tagged in the front as 'M' they removed the pin of the tag while billing. After I went home when I looked at the size back it said 'XXL' and the seal of the product is not opened. When I returned to the store immediately within 20 minutes and asked the staff about exchange the lingerie into desirable size. They said they can't exchange the lingerie and said the EXCHANGE POLICY is NOT applicable FOR LINGERIE.
What kind of policy is that? Is lingerie doesn't come under clothes section? and I even showed them the bill and the timing of the checkout. But, they said we can't do anything. why the customers have to face the loss for the mistakes of staff that doesn't tag the sizes accordingly?
It's not about the money is about how you're resolving the issues of the customer. I showed the bill, It's not even completed half an hour after the purchase, I clearly showed that the product seal is not opened and I'm not asking for refund, I'm asking for exchange. Yet the staff said They can't do anything. There is not one female staff to explain my problem clearly. If it's another clothing okay we can alter or do something, but it's lingerie how can we use large lingerie if it doesn't fit.
I'm so disappointed on the Reliance Trends.