Edgar's refuses to exchange my backpack

Im very disappointed at the quality of they bags. Towards the end of August, I bought a back pack for R350 on Laybye in Edgar's West Street now known as Dr Pixley Ka Seme street Central Durban . First week of September I used it and I discovered that the zip is faulty. Unfortunately I had lost my slip. So i put it aside. Then last week I was in Galleria mall and did an inquiry on it. The lady that helped me informed that I can get it exchanged, because I did a laybye they will pick up my details on the system using my cellphone number or my ID number, especially within six months of doing it. The following day I went to Edgar's in Central Durban to exchange my backpack. I was informed by staff and the manager that I can't get exchange because i dont have slip. I did inform them that it was laybye. They said it doesn't matter, I have no proof that I bought it from them. I asked them to check my details on the system, the manager and his staff refused. They told me that the laybye gets deleted after I take it out. 🤔 The manager then took a photo of the bag and said he is putting it on group chat to ask the other managers for a quote. When he gets a quote he will phone me. Im still waiting up till today ☹️. I would like to find out why two stores from the same group have different policies?