The WiFi Assist feature of iOS 9 should affect "only a small" percentage of your phone's data.

This was the assurance made by Apple on its newly-created support page explaining the "ins and outs" of the iOS 9's new feature, reported The Telegraph.

"Because you'll stay connected to the Internet over cellular when you have a poor Wi-Fi connection, you might use more cellular data," the support page said.

"[But] for most users, this should only be a small percentage higher than previous usage," the page added.

The WiFi assist feature, which was included in the iOS 9 software update released by Apple last month, is designed to automatically turn on your phone's cellular data in instances when the WiFi connection is poor.

But because the feature is automatically turned on by default when the i0S update is downloaded, users have complained that they have been "tricked" into using more cellular data which go beyond their regular plans.

Some have taken to Twitter to vent their frustration.

"Damn WiFi assist. 4 gigs run dry when I don't need you," TJ (@TJ_desu) tweeted.

"Thanks to WiFi assist I successfully exceeded my 4GB data plan and used 5.4GB," Joey (@Joweeeleee) posted.

To turn off WiFi Assist in iOS 9, users only have to open the Settings app, elect Mobile Data, scroll to the bottom of the menu, and toggle WiFi Assist to off.

In the meantime, Microsoft explained that WiFi Assist doesn't activate with third party apps which stream audio or video or download attachments, like an email app, according to the Independent.

For instance if a user is playing music on Spotify and the Wi-Fi Assist on, the feature is not going to use all the data streaming the song.

"You can use WiFi Assist with most apps like Safari, Apple Music, Mail, Maps, and more," Microsoft's new support page for its latest iOS 9 update said.