Bad service

I went to Woolworths Baywest to buy pair of school shoes! Firstly not all sizes on shelf, no one to assist! Asked cashier, she checked on system, there is in stock room. She asked another staff member to go fetch, she rep****, stockroom already locked. Cashier told her I need size 5 and she can see there is in stockroom. After half an hour she came back with size 5! I went back the following day to exchange for size 6, security tells me to fetch right size and go upstairs to customer service. No size 6 on shelf! Went to cashier again ask if there is 6, another lady came and said I must go to customer service, she wil fetch 6 and get me there! I went to customer service, after tried to explain to cashier someone went to fetch 6, she still does refund and give me my money back! For retailer this big, customer service is pathetic and why not all sizes on shelves???