Was the entire ring torn off? I had a section chip off and was able to glue the piece back on. It held long enough to remove the bolt. If that doesn't work, needle-nose vise-grips holding the bolt and a wrench applied to the vise-grips may work. There are also nut extractors sold at Sears, but I didn't see any larger than 19mm which won't fit around the wheel lock bolt. A tire store or mechanic may be able to pound an impact socket over the bolt to get enough grip with the impact wrench. Good luck.