Facebook notification problems on iPhone?

I recently got a new iPhone 4S. I downloaded Facebook and I can use that app fine. However when I open the app it says I need to update my password for my account in the settings. When I go to do this, it says that it does not recognize my password. When it asks for my account name it automatically says my old one. (I changed my "facebook username" a few months ago.) I have not found a way to make my phone recognize it yet. I've entered the correct password numerous times. I have tried changing my password, using my old passwords, restarting my phone, deleting and redownloaded the facebook app, logging off and back on, waiting a few days, and checking for the latest version. I have no clue why it's not working. Any suggestions!

Its Probably a Error With Facebook you Can't Fix This Please Contact Facebook at the Help Center and Report the Problem to them

You need to contact facebook at the help centre and report the problem.