Still wi-fi problem

From the same document

If you are still unable to turn Wi-Fi or Bluetooth on or off after attempting these steps, contact Apple or your wireless carrier for additional assistance.

Could be a hardware problem

I walked into the Apple store today with exactly this problem on iPhone 4S. I had tried everything, and I mean EVERYthing, nothing worked. Genius took one look at phone (greyed out wifi button), said it was irrepairable – logic board failure – and phone had to be replaced. Cost £139 for new handset because out of warranty.

Google for a local iPhone repair person not employed by Apple. There are some good ones who are not so expensive.