4G mobile data being used even when mobile data setting is off? I have a Motorola Moto G, the 4G version, with the original ROM upgraded to the latest version (4.4.4 official from Motorola).

The first thing I did when I got it was the same I have done when I got my previous phone and every time I (re)installed a ROM on it: disable mobile data, so that I don't get charged by my carrier and instead use only my home wireless network.

Despite the above, I just noticed that I am being charged for several accesses to the network. Oddly enough, if I go to the data usage screen on the mobile, it says no data has been consumed since I bought it, which is what I would expect. Yet, my carrier says that in total, since I got the phone 20 days ago, it used a grand total of 1 (one) Megabyte in several very short communications.

When I called customer support, they told me that data traffic can still be consumed if I have the phone on 4G, even with the mobile data setting turned off. WTF?! I may be wrong but I find this pretty much impossible to believe. As far as I know, this is impossible - mobile data off means mobile data off; nothing will be transferred, not even in the background, am I right? Or is it possible for something to slip through somehow?

Even better, he told me this is the information they have from the manufacturers themselves, and that several people have been complaining about the same. First of all, I doubt the manufacturers would say something like that because I don't believe it's true. Second, I suspect that these are cases where people have both wifi and mobile data on, and when the phone goes to sleep, the wifi gets disconnected and the phone naturally starts using the mobile connection.

To top it off, the tech support guy told me that if I turned mobile data on, set the connection type to 3G and then turn mobile data off again, it would no longer behave like that. I was waiting for him to tell me that afterwards I'd have to press up, up, down, down, left, right, left, right, B, A...

He also mixed the concepts of 2G/3G/4G (cell network type) and "mobile internet", not realizing that the type of cellular network, and accessing the internet over that cellular network are completely different things, so I'm taking what he said with a huge grain of salt.

I've been searching for quite a bit now and the closest reference I find to a similar problem is in a post here but I don't have the GPS on (as stupid as it may sound, I didn't even know how to access the GPS on this phone until I saw that post and wanted to make sure it was off).

Besides a problem on the carrier side, does anyone have any idea about what might be causing this? Is it really possible for data to slip through while using 4G and having the mobile data setting off? If so, how, why, what does the cell network type has to do with it, and how do I stop it?
This has been happening throughout the world and is caused by a technical feature of 4G LTE. Most people don't even notice it because of the small amount of data that's used off their data plan. This is what happens: every time your phone receives or makes a voice call, it automatically switches from 4G to 3G mode due to the fact that LTE is a data-only technology. When the voice call is ended, the phone switches back to 4G mode. You may have mobile data disabled and restricted and yet this switching back and forth from 4G to 3G uses small amounts of data each time. You can prevent this from happening by setting network mode as WCDMA/GSM. So it seems that tech support guy knew exactly what he was talking about after all.