Broke my water pump bolt. Now what? (Update - broken bolt is out)

You should’ve followed post 23 and the center of the bolt would have been established.

“Do you have anyone with access to a lathe? I’d take a bolt the size of the broken off one and drill a hole through the center the size of the hole you would be using for an easy out. Then thread a nut on to the bolt that is broken off and thread the bolt with the hole in it into the nut. You can then use the bolt with the hole as a drill guide. If you don’t want to use an easy out that’s fine because at least you have a centered hole to use to progressively drill the hole bigger until you can barely see the threads. Sometimes you can get lucky with the reverse twist drills while doing this and the bolt will back out while your are drilling“.