LG G4 overheat when wIfI IS ON AND DRAINED BATTERY

I bought LG G4 with my previous carrier T-Mobile. I never had an issue. I love the phone; however, recently I change carrier to AT&T and the overheat issues and battery drained with my wifi started. T-Mobile doesn't want to deal with my phone. AT&T is "no comprendo" or basically this phone is not ours. I contacted LG and after several tries and procedures testing they asked my to reset to factory default which I did. Now my LG G4 still overheating when I use wifi and the battery drained.

Any suggestion other than to buy another phone? I would greatly appreciate any help.

Thanks,

Bernard

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