Why pay for Resize?

I have bought a ring from Sterns Sasolburg and they didn't have the size I needed, so apparently they want to charge me R300.00 to get the ring to the correct size. I mean how is that my fault that they do not have all the sizes? I paid for the ring already and I don't understand why I should pay for resizing.. I mean which store does that?? Furthermore, on the paperwork I received it says they sent it for repairs. How in the h## # is that a repair as if I have damaged the ring?