My bathtub I have tried just about everything to clean it to no avail

If the finish on the surface is worn (sounds like it is a porcelain finish old tub - new ones are very expensive) no amount of scrubbing in the world will get it clean looking enough. If Barkeepers Friend doesn't work then it is time to consider having the existing tub reglazed or replaced.

I don't know what you have tried or if jinatty is correct but if just dirty you might try bar keepers or Ajax's with white vinegar not much water and a Mr clean magic eraser a lot of elbow grease will clean any thing off will not fix bad finish

Have you tried a mr. Clean Magic Eraser? Also I use straight Clorox bleach in a spray bottle when all else fails that usually helps

Try some east off oven cleaner

Try some Kaboom. Spray it on let it sit for a few minutes for the fumes to dissipate so you can breath then scrub with a plastic scratch pad or a magic eraser. Rinse thoroughly. Kaboom is some good stuff! We have a lot of lime in our water so our shower gets a real dingy grey color from the lime deposits and soap scum which clings to our walls and tub then turns hard as a rock but kaboom takes it all off with some elbow grease and a plastic scratch pad. Our shower is acrylic so you don't want to put a lot of pressure on the scratch pad as not to scratch the acrylic finish. I've tried so many things that didn't work but am happy with the Kaboom.

I have an old porcelain tub and I got Sick and tired of trying every concoction under the sun and went straight for the Clorox toilet cleaner. Did wonders! I have no idea if this is recommended, Or even safe, so do your research first to make sure it’s ok....I wouldn’t use it on any other type of tub.....also, lots and lots of air ciculation the fumes are pretty bad.

I make a paste of baking soda and hydrogen peroxide. I let it sit in the tub or sink for a while, it usually whitens my old porcelain sinks and tub really well.