Looking at the Arduino UNO product page on this very site shows the SDA/SCL on the back like the original poster has.
But the OP is not using an original UNO but an (illegal) clone. We've often seen clones that have labeled pins that doesn't have that functionality. So just because your original Arduino UNO works with these pins doesn't mean the cheap Chinese copy does too. But CrossRoads is correct, the OP can just use A4/A5 and he's fine.