Software issue? on iPhone 7+

Hi ,,my iPhone 7+ went wrong yesterday. I first thought my phone had been hacked so I rang apple support for help. I spent over two hours on the phone to an advisor, trying to get me phone to work, but everything failed. The phone wouldn't recognise my Apple ID or my wifi password. Tried everything. The advisor on the phone thinks I have a software problem on the phone. The call was ended with instructions to back up my iPhone to my MacBook Pro then do a factory reset. However when I tried to back up to my MacBook I got an error screen saying iPhone had "no value". So I couldn't do anything. I rang apple support again but still no further forward.

I would normally take the phone to an apple store and get the staff to take a look at it - but due to Covid-19 I can't :-(. So at the moment I have taken my sim and put it in an old tiny iPhone, which is not very uptodate and the screen is tiny !! ....

I really need my phone to work - what do I do ??? Can you help ???

Kind regards

Jennie