Factory reset your phone to fix this issue:
* Ensure the device is powered off.
* Press and hold the Power button and the Volume Down button (located on the right edge of the device) until the Sony screen appears then release.
* From the System Recovery screen, select Factory Reset.
* Select Yes.
Hope this would fix your issue, if still issue exists then check [http://guideusermanual.com/product-name-xperia-z5-manual&po=570042&lang=English|Sony Xperia Z5 Manual.] for more ideas.