Every new building undergoes diffential settling of floors if constructed on a pier and beam footing system. Within two years all final settling should have occured and cracking should be minimal.
If after that time you have found that a) the movement was extensive, or b) the movement is still occuring, then you should look to whether a geotech report was done for the area before building. Not all soil tyles are the same, and cohesive soils need to be using different piering systems.
Consult with the Engineer who designed and stamped the structural system of your house and talk to the local council who checked and approved the construction. If you are not happy with the answers arrange to get a separate geotech appraisal done.