Edgars promenade

I went to edgars promenade to exchange a pair of takkies that i bought at Highkey which was at the time part of the edcon group. The takkies has a defect and I've only had it for 4 months. I took it to Highkey who then told me i should return it to an edgars store. I went to edgars to return it and the cashier didnt want to help me and said i should take it to Highkey, after i explained to her what they said at Highkey she told me shes going to speak to her manager. The manager then said okay its fine i can go and fetch another pair of takkies. The price of the takkies at highkey was R799 and edgars price is R849. After a long argument with them that i shouldn't be paying extra as i am coming to exchange it and that i should get it for the same price i originally paid for it the cashier and manager then insisted that the R50 should be added to my account because i didnt buy the takkies by them and their price is R849 and that they are doing me a favour by exchanging my takkies as it was bought at Highkey which was at the time part of edcon