Truworths, Tman tshirt low quality

I bought a Tman tshirt and after just a few wash, the neck part shows this stain or line all around the neck as if the tshirt is dirty. I didn't expect such from Truworths clothes, even clothes from much cheaper shops do not show such, you can wear their clothes for years until you even get tired; these Tman tshirts from Truworths are a disgrace. When I tried to take it back I was told that I should have returned it immediately. I have bought a lot of clothes from Truworths which were of a very good quality and I was expecting the same quality on this particular one.