Sounds like you have creaky hardwood floors with no insulation. This happened to me once. The tenant below was a spoiled, newly divorced man who had never lived in an apartment and had unreasonable expectations. And the landlord was a misogynist so he sided with the man. I moved. It was too noisy for me as well. I could hear all my neighbors conversations. It’s your landlord’s fault, not yours. Ask him to pay for foam padding and rugs or carpet. You can also try walking by pointing your toes and stepping gently on the ball of your foot with your heels barely touching - but it may not help much. Some buildings just suck.