A few weeks ago I dropped serving heavy on my foot. The bruise is gone but a tender bump remains. ?

May be a calcium. The bone lives on its outside surface like bark on a tree. If you dropped something on a bony surface, you do not have to break bone to get a reaction. A marred bone may put on a bump called a callas, composed of bone fixers and blood that creates a knot that may last quite a while. Some bruises will also form a pocket of calcium that may last for quite a while also.
Bone. If lump remains it needs to be checked. Possible bone contusion or other bone problem or a soft tissue mass that developed secondary to original injury.
Foot pain. Pain is not normal. If you feel it's lingering even if no swelling nor bruising, pain is your indication you need to see a doctor. I'd recommend asking about possible contusion to the location foot. You may need an xray to rule out other pathology. I hope this helps.