How do I stop water constantly running, never filling up in my toilet?

Keep adjusting the float until the water shuts off at the proper level. The water level in the tank is controlled by an adjustable float. A float that's set too low produces a weak flush; if it's set too high, water spills into the overflow tube and the fill valve won't shut off. The toilet keeps running.

Have you checked inside the toilet bowl to make sure the chain isn’t stuck?

ALSO check the 'flapper' to make sure it seats itself after flushing and nothing is hitting or blocking it from closing.

take the lid off the back of the toilet and look at the rubber flap on the bottom is the pull chain caught in it, if so tighten the chain, if not turn the water off and feel the flap and try to remember how old the toilet is you might have to buy a new flap if it feels a little mushy or a lot of black comes off on your hands the flap is the cause of most of running toilets, also look at the innards, is it a large ball on the end of a rod, if so try bending the rod just a little bit so the ball is a little higher, and lastly if it is a small plastic tank on the end that raises and lowers with the water it should have an adjustment place on it a, if all that fails to stop it then you have to buy new innards, probably around $20 a lot cheaper then a new pump, hope this helps xx

My suggestions were the same as all of the others. It’s easy to replace the whole thing.

If the water keeps running even after the float valve should have shut it off, it may be mineral buildup inside the unit that is preventing the valve from closing. Almost all fill valves have a top that can be unscrewed revealing the rubber flapper that acts as a valve. Before opening turn off the water. If you see grit or white mineral inside the valve remove the parts carefully, rinse them off and put them back as they were.