Most disgusting service

On the 4th Oct 2017 I went to exchange an item (Racerback Racing Skin Costume) for a correct size at Mr Price Sport The Glen. It was still early in the day for so expectation would be that the stuff are happy to give one good service as they should. I stood at the door with a plastic on my hand visibly showing its that of the store in question, waiting to be approached by one of them none of them attempted to approach me, they all stood inside the store near the cashier and plain blanked stared my direction with no sense of care whatsoever. I then decided to then walk into the store to the one lady that had stared, she just looked at me no greeting and no care in the world to ask what is it that she would assist me with, I then took it upon myself to greet then explained that I would like to exchange item for a suitable size (One size bigger) as the size I took wont even go through my thighs as expected as its meant to expand due to the material but that was not the case. The woman then said to me she wont refund (sign that she was not interested in what I had requested) I then had to explain to her again that I am not interested in getting a refund all I needed was an exchange. I asked to speak to the store manager as she was not being helpful, she then advised that she will call the manager, she then took the plastic with item inside walked to the till area swinging the plastic bag then just chucked it on the table behind her, following that she then called the manager. The manager came explained what I had explained to the rude staff member, that the size was one size smaller and that I doesn't even fit on my thighs, bearing in mind that there was still a slip on the item. The way I was desperate to get a fitting size I went as far as telling her that I can even demonstrate that I never wore the item by fitting it in front of her. She took the item out of the plastic then looked at the size and to check if tag was still there, and indeed the tag was still intact. She then looked at me as said don't I know what my size was, why did I take a small size if I know very well that I am FAT (I was with my 9 year old daughter) when the manager body shamed me in a very demining way. I have never ever came across such disrespect in my life. I stood and started at her with disbelieve and shock in my eyes after saying that I am FAT. I then took the item without saying anything and tears rolling down my face as I felt disrespect in no measurable way, after spending more than R1200 at the store (I have a receipt to prove it) . With that said I would like to lodge a formal complaint and this issue be addressed.