try this: https://www.craftylittlegnome.com/clean-toilet-coke/
a cleaner called Zud.
Use a pumice stone on the stains. Just make sure it is wet first or it will scratch the porcelain.
My solution was the pumice stick. This is excellent way to remove stains and rings in the toilet. When commercial toilet cleaners fail -this is my go to. Great for thick crusted calcium mineral build up that the toilet waterbowl collcts.
They are found at my local Walmart for less than two dollars -good for multiple uses.
Be sure to follow the use instructions, soaking the pumice stone in water for a few minutes. While the stone is soaking, grab your toilet brush and splash water up around the ring. Note: It’s very important to keep both the stone and the surface wet while cleaning to avoid scratching your porcelain.
Janice: I've had good luck with something like this: