Passenger Door Not Unlocking

Hello,

Sorry if this has been posted a million times.

Just went to move my car out of the company car park and noticed that the passenger door would not unlock with the fob.  The only reason I noticed is I sometimes get in and out of this door as I park up close to a wall on the drivers side.  

Annoyingly once I had got in via the rear passenger door I tried to open the passenger door from inside but broke the internal handle!  Really did not apply much pressure and was surprised that it broke so easily.

2 Questions - Is it straightforward enough to replace the internal handle?

What could be the cause of the door not opening?

Thanks