Flabbergasted with service

I have bought a pair of tackies about 2 weeks before Xmas which was only worn about 5 times (not a full day). I paid R299,99 for them only to note last week that the sole of the tackies are coming loose (you can actually see it as the sole is a different colour to the shoe). Today I took it back so that it can be exchange for another pair or something similar only to be told that I can't exchange it as it was worn. Obviously it was worn . I find this pathetic service as I always buy by them. I am not asking for a refund but only an exchange. If this is the services I am getting, this account will be closed.