Why does my player keep going through the terrain?

Hello, I have a little sphere which is supposed to swim around in the terrain. However when ever it is goes down and into the terrain, You would expect it to just collide with the terrain and not go anywhere, however it goes right through it. The sphere was exported as an .fbx from blender and when I imported it in. I checked the box saying "generate colliders". At this point I'm stumped. I added a collider to my sphere and the terrain has a terrain collider. The terrain is also not checked as a trigger. This is bugging me so much and it would be so nice if I could get an answer. Thank you for you time.