SHOCKING customer service.

Having tried on and bought this dress, I wore it and washed it. After the first wash the material had frayed under the arms- on both sides and holes started to appear.
I was still within the time to return the dress so I returned it to the Bury store. I asked the shop assistant if I could have a refund as it was obviously a faulty item. She went to ask her manager then came back and said that it looked like the item had been stretched- implying that I had done it. She could only give me an exchange in store. I was embarrassed and felt like she and the manager were implying that I was too big for the dress. If it didn't fit me I would never have bought it so that was ridiculous. A £46 dress should not fall apart that quickly and the material is obviously shoddy. Topshop WAS my favourite shop and I had always felt comfortable shopping in their stores.
I made a complaint to customer services via email and after having two people reply to me saying they were going to "look" into the matter, I received the latest one saying that nothing can be done. Shocking customer service. NOT HAPPY.