No access to contacts section

Nokia X2-01 RM709 won't open the Contacts stored on the phone and the screen freezes when trying to add new contacts to the phone-book.

I also wasn't able to backup the phone-book using Nokia Suite. Nokia Suite would fail to backup after a while every time.

I tried "Reset Settings", "Restore Factory" and at last flashed a newer version of firmware, yet none of these fixed the problem.

I'm starting to think it's a hardware fault but I don't know where to start.

Any Idea?