My iPhone 4S will not connect to the wifi, it greyed out the switch.

Ok, so just after Christmas, Mum got a new phone. She gave her old one to me. All the wifi and everything was working perfectly for the past 2 or 3 years we've had the wifi.

We also got a new Playstation 3, and we connected it to wifi a while after. A bit after that, my phone experience just went downhill.

First it started saying 'unable to join network' . So I turned it completely on and off again. When I went back into wifi, the switch was greyed out. I turned it on and off a few more times. I then reset the network settings, though that didnt work. I then reset the whole phone after I backed it up to the computer and it still didnt do anything.

We went to Apple Genius Bar a few days after, and I got a new replacement one. Again, it worked for about 3 or 4 days and then it just all happened again.

It's geting really frustrating. Don't get me wrong, I absoloutley love Apple. The whole Android and Samsung stuff kills me. But this is really getting annoying and I really want to connect to the wifi.

I have tried turning off the wifi on other things, but it still refused to connect. I have turned the wifi box thingy on and off too.

Thats all the details I can think of that are important. Please, can someone help me. Im dying here \😢/