My Nokia Lumia 520 is stuck in flight mode, unable to make any calls. How can I get it out of flight mode?

[Windows Central Question]

My Nokia Lumia 520 is stuck to flight mode. unable to make any calls.

Phone software appears to be corrupted. Nokia Lumia 520 remains in flight mode. If try to remove, the Aero plane symbol keeps fluctuating. Tried formatting, does not work. May be need complete formatting and rewriting of the software