Woolworths refuse to EXCHANGE my shoe

I bought a pair shoe size 7 on the 18/04/2015 priced R199.95 code ( ***69 0507) ( ***68) and this is the size that I always take , however on Sunday when I tried the shoe on @ home and I realised that it hurts my foot , so I did keep it on for like 5 Min but it got worst, so I wiped the shoe and took it back to the store on Monday to exchange it for a size 8, the store manager named Nirvasha Krishnapersadh tells me that Woolworth's does not sell secound hand things and she cant exchange the shoe, she did not greet me or be courtuos in any way and I had to explain to her what had happend,she did not care and I told her I dont want anything else I just need a size larger and it is not my fault as Im a size seven and thats what I took , she then says to me well this is not leather it does not strech I should have noticed that, how should I know that, why dint the store had a board stating that please take one size bigger on this shoe as it is a small cut and the size may vary from your normal size to one size larger, so now because I dont have money and Need a shoe to wear I am forced to use this shoe and get blisters on my feet and be in discomfort, I will take out