iPhone 6 is constantly searching

After a visit to the apple store my iPhone 6 as been deemed damaged I wiped out with phone in back pocket, the back-plate took a bad hit and the iPhone 6 now as a bend to it causing a slack between the screen and back-plate (bottom only and snug at top). It has been fine ever since but recently decided that It would start "searching" Apple tech says this could cause antenna (he says attached to back-plate) to loose contact with sim card causing the phone to search or short(fried) the sim card. Not sure if that is possible. So we replace sim card, it worked for a 2 weeks it started doing the same thing, drop signal and search. So I started holding the phone and apply pressure at the sim card location (thumb on screen & index on backplate) during power cycle and to my suprise, the phone would lock signal work for a while then suddenly drop and search. Sadly this trick no longer work and the phone only work under WI-FI. i have tried holding at the bottom, top and middle without success.

What parts would you suggest I replace or perhaps check first before buying new parts.

I'm looking to replace only the bent back-plate but do I need more? antenna and such?. I'm confident in my skills to take apart my phone and rebuild with know good parts.

Is the antenna attached to back-plate? or am I wasting my time.

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