If it were just rust or some common gunk it'd be an easy clean. But unfortunately, polish....very stubborn. I've got a bottle like that myself that I couldn't get 100% clean.
Investing in a bottle brush might not be a bad idea if you haven't yet, or pipe cleaners, or anything that could physically get down in there. I've used vinegar and table salt and just shaken the crap outta it before.
Some crud will just not want to come out too, sometimes you just can't win. Just gotta try