Screen freezes constantly, replaced screen. Now black randomly

Hi All

I have an iPhone 6, just out of warranty...

A few months ago the screen started to freeze randomly. To unfreeze I press the sleep/wake button twice, and we try again. At the begining it froze from time-to-time, in a matter of 2 months, it freezes after about 20/30 seconds - but is spontaneous. '

After reading forum after forum, I had the screen & the digitizer replaced.

Now my screen still freezes, but goes black, or green with pixel lines everywhere. This made me think that a cable was loose, so back it went. They reconnected everything, and the issue's still happening with absolutley no improvement. Now i get about 20 seconds use out of the screen (if i am lucky) and thats it.

Back to the forums again... maybe a software issue?? So backed up the phone, removed all data. Full factory re-set. Loaded data back on. Same problem. So factory reset again and didn't reload the data, only signing into icloud this time. Removed majority of my apps, all new ones which had been loaded since the issue began. Same problem.

I strongly believe it is the screen and not the HDD, as when it freezes, if you are still streaming music etc the sound isn't affected, its just the screen goes black. As time has progressed it is no longer simple to correct by pressing the wake/sleep button twice. Now I have to press it once (to lock the phone), wait about 6+seconds, before pressing it a second time to wake. Most of time I just have a black screen and a useless phone.

Battery Life, Phone's CPU performance etc do not seem to make this issue worse.

I really dont want to have to get another phone... if i do it will not be apple. Although I love the iPhones, I have had far too many issues with these phones, and I cant justify another $1200 for a phone which only lasts 24 months.

Anyone had this problem who managed to fix it?

I am pretty desperate to find a solution.

Thank you!