Go to your nearest machine shop and ask them to look at it and give you a price on drilling or milling it out.If any of it is sticking out above the hole you can always try taking a pair of pliers and turning it out that way,i have gotten lucky a few times doing this.If none of these options work you can try a masonry drill bit to try and drill it yourself,but if it has to be drilled or milled out you probably will have to retap it a slightly bigger size.