Sorry for my poor english, i'm french ;-). I change my N4 backdoor. I agree with the fact that you must be patient to remove the whole backdoor. At the beginning, it's easy to open a breach, but to remove the entire backdoor, i take less than 10 minutes. I break an opening tool, i use my nails, and with my last plastic opening tool, i turn around the phone and i finally full open it. So be patient and do not force. Thx I fix it !