I have done everything that is advised above but my iphone 6 keep on showing “searching”

If you have gone through every step in here with no success....

If you see No Service or Searching on your iPhone or iPad - Apple Support

Then do as instructed at the end of the article.

Get more help

If your carrier confirms that there's no issue with your account or network, but you still can't connect to a cellular network, contact Apple Support.

If you see an alert next to No Service, learn what you can do.