Phone shuts down and starts with hard reset

Hi,

My Iphone 6 Plus phone is having a serious issue and I could not find any local repairers who has any idea on what the problem is. At the beginning of May 2020, I was having some problems with screen first as it becomes unresponsive or randomly shuts down, so I changed the screen to solve it.

Two or three months later, I started to experience random shutdowns again. Most of the solution proposals were related to battery replacement, so I bought a high quality(but not original) one. That did not solve my problem, but random shutdowns were not so often. However, they became frequent and more fatal as it stopped being powered on with power button. I start to use hard reset on every startup, and it usually also does not work nowadays..

Any idea why this should be happening and how it can be solved?

Some additional info about phone:

-It had touch disease fix a year prior to these series of issues started.

-I can see my phone on computer, it is being connected if I try

-Sometimes, it shuts itself down and does not open with power button or hard reset but shows me out of charge screen if I try to start it up hours or days later

-In cases when it is not starting up anyway, I put it inside REFRIGERATOR for 5-10 mins. It starts up after that. I don’t even know why I tried this(jedi sense?) and why it is working, but this maybe a clue to some experts, or maybe not..

-I tried restoring it back to factory settings, that did not worked.

Thanks..