Can you post the model number of the appliance please?
Is the door handle broken? Loose and floppy?
Is there a door locked light? If so, is this illuminated?
Model Number is XXXXX
No the handle is not broken
Yes there is a light illuminated.
OK, thanks for that.
Chances are it's the door lock mechanism that's failed.
Unplug the appliance from the wall socket, wait 5 minutes and see if it's unlocked.
If still unlocked it could be that the bimetal strip in the lock has stuck.
Give the front panel a good thump beside the door lock, see if it jars free.
If still locked, make sure you are still unplugged and take the top off.
Reach inside and at the front and you'll find the door lock mechanism.
Work it back and forth, side to side and keep trying the door.
Work at the lock gently enough so it comes off the screws without snapping.
Once it comes off the screws you can lift it off of the door latch pin and open the door.
You will need to replace the lock.
The alterntive is to use brute force and lever the door open. This will damage the paintwork on the appliance and you will need to replace the door lock and door handle assembly at least.
Good luck with it.
Let me know how it goes.