Not worth coming back. Its basically your manufacturing error. You need to own up.
Unfortunately, the tshirt I checked for the size by trying it out was perfect. Trusting your brand I removed and binned all the 3 tags, without trying the other 2 tshirts, thinking it would fit as all 3 are the same size (L).
To my shock and surprise, the 3rd tshirt I tried was much smaller.