bleach and kaboom, etc are not working.
A cup of vinegar in the bowl overnight...scrub and flush!
A crazy onslaught of every chemical known to man may work. =D Let's see: Comet, calcium remover, Mr. Clean, Scrubbing bubbles, Bleach, elbow grease, aslong as none of them contain ammonia (mixed with bleach it's toxic) that should be in order.
I had terrible rust stains when I moved into this cheap apartment. The tub too. I got a BIG can of Comet with bleach, put a lot in the toilet and let it sit overnight. Then used a common toilet brush in the morning and flushed. I also wet the tub and covered the ugly with a paste of the same comet, let sit overnight. Scrub the next morning with (actually the same toilet brush, the bleach sanitizes) and rinse with the shower head. 90% of the stain gone in the tub and all in the toilet! And only cost about a dollar and a half...
One easy way is to drain the water out, just turn off the water then flush what is left in the tank and bowl. Then add a 2 liter bottle of Coke/pepsi/storebrand cola. Let it sit overnight, scrub the walls a bit with it. Then flush it away. The other thing is to use a pumice stone (they are sold in the health and beauty isle, for softening feet. you scrub the stains with the stone, use a little baking soda with it. If you could have seen the toilet in my father's house after he passed away....Don't know what the cleaning lady had been doing, sure not cleaning anything but his bank account. We thought we'd have to replace it. The cola made it look brand new!
Another option would be to use dilute HCl on it. It goes by several different names. HCl. Hydrochloric acid. Muriatic acid. There might be a few other names that I don't know aboout. I'm pretty sure this would help whiten it back up, but if you use it BE CAREFUL! It's kind of like using super-bleach...sorta. Don't use too high of a concentration, wear gloves, wear eye protection, and make sure you flush a lot after using it to make sure it doesn't eat through your pipes. Definitely try the oven cleaner first, though. That sounds like it'll work just fine, but if it doesn't you can use this as a last resort.
As strange as it sounds, try the spray foam oven cleaner and let it sit 30 minutes before wiping it away.