"He who knows" is likely correct. What we use on oversized holes is wood. Break off some large slivers of wood from some scrap, pound then into the hole, cut the access flush with some side-cutters. Add more slivers if req'd, fill hole completely with wood, then use a wood screw as you normally wood to fasten your product. If you want to get professional, pound a 1/2" (sanded down a bit) dowel in there, cut flush to cement surface, then screw into as normal. 12mm = 0.47", so 1/2" dowel will be a bit too big, sand it down a bit.