iPhone 4 freezing on lock screen (iOS 7.1.2)

[gustavoskates]

I just got a brand new iPhone 4 GSM from the Store (I know it is an old phone but they still selling it) and it is freezing on a black screen when locked, it happens constantly and it started happening since I updated from iOS 7.1.1 to iOS 7.1.2. Please help! I don't know what to do i already tried this "fixes" :

*Turn it off and on

*Hard Reset

*Restoring from iTunes and setting it up as a new iPhone

*Restoring in DFU mode from iTunes and setting it up as a new iPhone

*Reseting all settings

But they seem to be temporary fixes because it still happening, and I don't know if the warranty covers that because it says for hardware issues

PLEASE HELP!!!!!

*NOTE*

When I said that it is frozen on a black screen I meant that the phone still on but it is locked and even tho I press the home or the power buttons it doesn't respond and I have to hard reset it to make it work again but the freezing come back after a few minutes or hours later.

(Power and home buttons working fine, like I said, it is a new phone)

iPhone 4 - iOS 7.1.2

 

[scifan57]

Since nothing you've tried so far worked, have you considered taking it to an Apple Store for a Genius Bar appointment to see if there's a hardware issue that's causing the problem? If there's no Apple Store nearby you could go to an authorized service centre for the diagnostic.

Also, all new Apple products come with 90 days of free telephone technical support. You may want to try that first.