iPhone 4 with IOS 9.3.1

Greetings

I have an iPhone 4 (not sure whether its 4 or 4s) that was working perfectly well.

Last week it updated to IOS 9.3.1 and is now not working.

I took it to the Apple Store in Chatswood (Sydney, Australia).

They tried to wipe it and re-install the new (latest) IOS.

The staff did some tests and agreed that it was not a hardware issue.

The initialisation process locks up after you select the Country then try to connect to a WiFi network.

Thats as far as it goes.

They were unable to fix it.

The solution was for me to pay around $120 a get a new iPhone 4.

They said they couldnt roll it back to an earlier version of IOS (seems crazy to me that you can't)

I would like the phone to work, I don't see why I should have to pay anything.

Any suggestions ?

Thanks in advance.