damaged goods not accepted

In January of this year I bought a pair or Class Act school shoes. At the beginning of March I returned them as they had literally fallen apart and they had a 6 month guarantee. Today I took that pair of shoes back as they too had fallen apart. The cashier told me that because they are replacements I can not replace them again. This I was not happy about so I ask for the store manager. The reply was that the store manager was out watching her son play rugby and will be back at 4pm. So at 4:10 I returned to the shop and waited til 4:45pm and still the store manager had not returned. this I find unacceptable. Now I am a single mom, who has just lost her job and can not really afford to go and spend more money on shoes for my son and I definitely can not let him go to school with broken shoes either. I have now had to go to another shop and spend money I dont have to make sure my son has shoes. I want action and a reponse