My iPhone software refuses to update. I have been trying for weeks. Every possible route, from Finder to iTunes, everything. I have had numerous people, who also own iPhone, try, and no luck! The last 2 upgrades do not work on my phone! Please help!

iStore - is that the one which is Apple authorised repair shop?

You have 90 days warranty for the repair. Take it back is my advice.

or

Check 

• you are on a good Wi-Fi, 
• on charge with more than 50% charged, 
• no VPN installed 
• low power mode turned off. 
• Fully working network connection via SIM.
• Check Settings, General to make sure you have no Beta profile installed.

It has been almost a month since the OP posted.

I understand but I get here three days ago I was absence for long time

How is it useless? If they indeed had their screen replaced at that store and it hasn't worked correctly since then the wisest approach would be to go back and available oneself of the warranty. Do you disagree with this?

LD150 also courteously listed all the possible issues that can come up when updating so the OP can check all of that. Those work about 99.99% of the time. And since the OP hasn't returned either using their warranty or following the steps listed must have fixed their issue.

So what would you post that would be useful?

Useless reply

Could you post a screenshot from the settings/general/software update please I think what’s wrong I had few people with the same issues and get fixed by me