Starter not engaging

Take starter back to have it tested, if it tests good then check your cables to make sure you have a good connection. If all else fails, have someone look at the flywheel

Ditto on the flywheel

your starter might have some damaged gears. If the replacement starter does the same then I agree, check the flywheel.

Also check to make sure the ground wire and the pos wire aren't touching . And make sure you have it all the way in and tightened so the gears can catch.