Perform a Hard Reset on your phone. That seems to be the only way out. But be warned. It obliterates all the data in your phone...and you will start everything all over again, just like you got a new phone out of the box:
Press and hold Volume Down and Power at the same time until you feel a vibration (about 10–15 seconds). Ignore the
slide down to power off screen.
When you feel the vibration, release the buttons, and then immediately press and hold the volume down button until you see a large exclamation mark.
Once the exclamation mark appears, press the following four buttons in this order: Volume Up, Volume Down,Power and Volume Down.
Your phone should now reset and restart itself. It might take a while for the reset to finish. You should see gears/cogs turning on the display, to signify the process. It might take a while to finish.
This will DEFINITELY resolve your problem, but, at the expense of your data in your phone. You will have to re-download apps. Stuff like texts, contacts and pictures are automatically backed onto OneDrive if you signed into your phone with a Microsoft Account, so you can recover that by signing in with the same account into your phone again after the rest. All the backed upp data will be restored.
You can check further instructions on How to perform soft and hard resets in the linked article