Rossmann Denied My Right to Exchange a Women's Tank Top

At the Rossmann store in Manisa, Turkey, I wanted to purchase a women's tank top. There was only one size 'S' available. I took the 'S' size tank top to the cashier and asked if I could change it if necessary because there was no fitting room. This was a rhetorical question because only bottom undergarments are tried on or exchanged in all lingerie stores. I am aware of this, but I felt the need for confirmation for some reason. The cashier, who appeared to regard herself as less authoritative or senior, asked another female staff member standing in the corridor if tank tops could be exchanged. The employee turned to face me and confidently stated, 'It cannot be exchanged.' I explained that only bottom undergarments are not tried on or exchanged in any store, whereas upper garments can be exchanged. This is governed by laws and is consistent throughout. She insisted, however, that they have their own rules and that the tank top cannot be exchanged. She said it with an almost comically high level of confidence while also being disrespectful. Of course, I abandoned the product and left the store. However, I believe that the woman in charge/employee at the Rossmann store in Manisa must fill the knowledge gap in terms of professional/communicative skills as well as legal aspects.