Unhappy with a Cole Haan brand and poor customer service

My partner and I have supported this brand and store for past 3 years. More than 12 pairs of shoes.purchased. The price of the shoe is usually high and we don't mind to pay for quality. In the last week of April 2025 we purchased 3 pairs of shoes. One of the shoes was a pair of ladies heels. I asked for a size 3 as that's my size. I requested both pairs to be 3 while my partner bought a pair of tekkies for himself. I went out of country and returned a week later after the purchase. On the Sunday 4 May I used my shoe for the first day and found it slipping off my foot. I had to continue yo wear it as I had already left my home and went to church. I walked from my car to church which a distance from the parking then decided to take the shoe back. I got to the store and found 3 assistants there. The guy that I bought it from was about to exchange after I explained until a female assistant just butted in and said no. In my rage I asked the assistant to check my account and see how many times we bought then he asked me for the box. If you buy a shoe for around R1700 would you plan to carry the box the first day you wear you thinking you will need an exchange. They continued to say they cannot assist me and asked a silly question as to how do I expect them to resell a used shoe. I left the shoe on the counter and left. A week ago I went back with my partner and the assistant has an audacity to tell me to take R1700 to Levingers and ask them to tighten the strap. We refused. He then said here's our head office email address see if they can help you as he tried and head office said no. I was so angry. We left the store. That was our last purchase and will never use that brand again. Admit when your product is not up to standard when a customer complains and never ridicule a customer. If I asked for 3 as I fitted on the 3 why does the box say 3.5. Whose mistake is that.