Q: iPhone 6 9.3.4 compass not working

All of a sudden I noticed that while typing anything, the message 'undo typing' would keep popping up and even when held upright, the phone would go into landscape mode. The phone also started losing battery power at an alarming rate. After charging it fully before going too bed, the phone was at zero battery level in the morning!

After doing a bit of research I realised that the problem was most likely related to one of the sensors that controls the compass, and sure enough, when I opened the compass app, it wasn't working. The compass wouldn't move at all and would just show -- instead of the the direction. Though the + in the centre would move when the phone is tilted.

The phone currently loses battery at an alarming rate - from full charge to empty within a couple of hours.

What can I do to resolve this issue?