PLEASE HELP: 2010 Mazda 3 gas gauge shows empty but gas tank not empty

[ZoomZoomZda]

Hi, I got a 2010 Mazda 3 GT. Yesterday when I started my car I noticed the engine light on, and when I was driving on the the highway I noticed the digital gas gauge gradually dropped from a almost full tank shown to empty within half hour. While the gauge reads totally empty I kept on driving and drove all the way home without issues. The car runs normal despite the wrong empty gauge reading.

Does anyone know what is wrong? Is it the fuel sending unit, gauge, or wiring problem?

If the whole fuel pump needs to be remove/replace do I need to drop the tank down or can I remove it from the rear seat cushion?

Any HOW-TO or video would be appreciated.

Thank you!

[ZoomZoomZda]

No one can help me with this or had this problem before?