Vishal Mega Mart — non replacement of shirt bought from vishal mart phase 5, mohali

I bought two shirts in scheme buy one get one free o n 15.05.18. One shirt wad regular fit and other was slim fit. I gifted one shirt (Regular) to my known. When my husband tried the ither on next morning it was slightly tight. I went vishalmart on 16.05.18 with bill to replace shirt. But tbey people said that we can't change as this is put in zero value in bill. I have to bring other shirt also. How can a customer know that which product is being billed as zero value and which is being billed at full value. I requested very humbly to replace but they totally refuse that they are completely helpless. It was a huge harassment to me. I request to direct them to replace my shirt or give me compensation for harassment. This is totally fraud.