please help me battery and overheating issue

[lollixo]

hello guys i want to tell my story with this phone. i bought the phone this july the firmware installed was 52.1.A.2.1, i came from the xperia xz1 compact. after turn on the phone i immediately installed my app with releated configuration. the phone was fantastic, after 2 days, i reached 6 hour screen on time (with remaining charge of 44% I swear!): surfing the web, installing app, watching videos, doing some photos and videos. all this use without experienceing overheating. also the next days were great too! and than arrive the new update, without worries i updated the phone, and since than the odyssey started. until that days, i perform this experiment:

-format the phone, and started again without restore my old datas
-repairing the firmware with companion app
-downgraded to 52.1.A.2.1
-i tried to use the phone in the "secure mode" like a provvisory mode
-the last step was downgrade to android 9

nothing of this solved my problem! the phone get overheat after few minutes of watching live events (streaming), or surfing web.

this morning i started with 100% and now after this:

google play services 20 min
adblock browser 80 min
screen 150 min
tapatalk 5 min

i'm at 33%!!!!!!

i want to know, how it's possible? some of you experienced this? yesterday i installed android 9, if after one week the situation will not get better i will send the phone to assistance

please, please help me

thank you so much in advance