It is possible that the issue is related to the WiFi chip or an issue with iOS software. To rule out iOS glitch, you have to restore it from iTunes on your computer. If this is related to software , then restoring the iPhone will fix it. But I've to warn you. If this is hardware related, there is a chance that the restoring will fail and your phone may brick which may render it useless. Since you already tried resetting settings, restoring is the only option left.
First download and install latest iTunes on your computer from here : https://www.apple.com/itunes/download/
Then connect the iPhone to your computer with the USB Cable.
Open iTunes application on your computer.
iTunes will recognize your iPhone. Select your iPhone in the top left (select iPhone icon)
Then in Summary section, click Backup and make sure "To this computer" is selected. Let the Backup complete. Do this backup one or 2 times.
Then click Restore button and let it restore. It will take some time to restore the iPhone .
After restoring, you will get option to restore your backup. Select Restore from iTunes backup and all your files will be restored. If this is software, then this will work.