Ideas for getting into wall
You may be helped out by getting a bit extension, it sounds like you have standard tools, I currently live in a 30’ farm house, drilling to put a new sub in took close to 18” I had a son make measurements and thought 12 would be more than enough, ended up adding a set screw bit extension as I had to drill down in this case inside a cabinet . We got the feeder in but it took longer drill bits than any new home could even imagine, so find an extension if drilling straight and this is important straight down, because a slight angle you can punch into a room, not hard to fix but easier if centered and plumb.