Hola The problem could affect anyone who has upgraded to the new iOS 9 operating system, even if you don't have the new iPhone 6s or iPhone 6s Plus as when you think you're using Wi-Fi it may automatically switch you to your phone's data. Warning! The new costly setting explained The new feature in question is called 'Wi-Fi Assist' which the settings clearly state will "automatically use mobile data when Wi-Fi connectivity is poor". If you have iOS 9 the default setting is that this function is switched on. This will use your data allowance much quicker than you may expect, and in the extreme, could mean you have to pay for extra data if you end up above your limit Davexf

Thanks for posting that Dxf.

Here's how to turn it off.

How to turn off iOS 9's Wi-Fi assist to save your data plan | Macworld

This subject should really be in The Lab, but I will leave it here as a warning to any IOS9 users. As there is little more that can be added, I am closing the thread.