My toilet bowl has developed rust stains and i can't get rid of them. Know any causes for it? solutions?

I already tried different cleansers and rust removers, but the stains only fade a little. Is it hopeless?

You need to use a bowl cleaner that has Hydrochloric acid in it. Just read the labels on toilet bowl cleaners. Plunge out all the water you can ,add it to the bowl and use a brush. It should be gone in seconds. Be cautious when using this chemical don’t get it on your skin or in your eyes and don’t inhale it. If it is not gone in seconds keep brushing the chemical over the surface. This will work. You may have some spots that the brush will not get well or if it is crusty or hardened you can use a razor blade to scrape it it will leave gray marks which you can remove with comet very easily. But don’t mix these chemicals together!!!!