Big Bazaar / Futurebazaar / Future Retail / Hometown — purchased dress in smaller size, and want to replace it bt lost my bill

Address: 700013

I purchased two dresses total worth rupees 1301 on 29th september, 2018, and i have purchased the smaller size. but i have lost the bill.i called the customer care service they told me that i cant exchange the product if i can tell the price and what i have bought together, can they give me a duplicate bill? how can i exchange the product? do they help me to exchange?