Problem with my nexus 6p

I think this problem surfaced ever since i downloaded the beta update for Android 7 on my Nexus 6P device. My signal coverage and internet speed ( LTE/4G/3G) started fluctuating on its own and now the condition is so bad that i haven't found any signal connectivity for the network that i use even though other users of the same network in my area are having connectivity. I tried to insert that sim on another device and it worked just fine. I have taken every measure possible, restarting, doing factory reset, downgrading to Android 6 etc etc, i just wanna confirm if there is something else i could do or giving it to the service centre is the only option left?
I cant even tell if the SIM card slot is broken because the notification bar does not show me the error that the SIM is missing or whatever, it is reading that there is a SIM card there, i'm just not getting the connectivity...
HELP ME! I LOVE MY PHONE WAAY TOO MUCH!! I DONT WANNA LOOSE IT FOR SUCH A LONG DURATION!:(:(:(:(

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