Damaged shoes and they refused to take them back

My mother bought 2 pairs of shoes and rage. She wore the first pair and on her way to work she realised that the right shoe is not comfortable she immediately took off the shoes and wore a different pair. Today we took the shoes back and when we get there, firstly the cashier was really rude and her voice was raised to the top of the ceiling secondly they refused to accept the shoes because she had worn them but they could clearly see they were still brand new. After she called head office we were advised that they could not accept the shoes back and there is nothing they can do. So my question, are we not allowed to tell them that their shoes are of bad quality and why could they not let us exchange them? My mother was furious and left both the pairs in the shop without and exchange or a refund.