If it really wont come out with anything, as a last resort you could try some cerium oxide glass polish on a DA or drill, it will polish out scratches in the glass so should take care of those spots too. Careful if you use a drill though, keep checking its not heating up too much as you go along.
As above though you could try a blade, maybe use some quick detailer with it to minimise the risk of scratching.
Sent from my iPhone using Tapatalk