We don't know what could be wrong since we can't see how you installed it, re-read the instructions and try again. If you are sure you followed the directions properly a second time, the ring could be faulty, contact the vendor and/or try a different brand.
Thank you. I found out that with Canon you have to set the aperture with the lens attached in the normal way, press the depth of field preview and then remove your lens, add the reversing ring, reconnect your lens (reversed) and there you go. Limited obviously but better than nothing I guess.