What does whatsapp charge for international calls?

(mobile post-paid, USA)

Just had a chat with AT&T representative and it left more questions than clarifications. Worst of all, it also left a hole in my pocket since we're been charged to international calls we never did.
Issue: we found charges for international calls in our latest bill. We recognize the number called, but we never call international, we always use whatsapp and/or facetime.
Here's what 1st AT&T agent told us (copied/pasted from the actual chat):

Ken: Using whatsapp with cellular data will count against your cellular data
Ken: That is why you've been charged for INternational Long Distance
Ken: I was able to verify that the International Long Distance charges on your bill is valid due to
using cellular data while calling even using 3rd party app
Ken: The time it will not be counted against your data plan is when you're using Wi-Fi
Ken: I would love to clarify this for you. If you're using cellular data using communication
applications, it will count against your data plan unless you're using a Wifi.

So, using whatsapp to call international will co$t money. And, the agent VERIFIED that the charge is for using a 3rd party app. That would explain the charges... even though... we've always complained that whatsapp doesn't connect when we're not on wifi... it just doesn't work... we thought its a lock in the app or something alike but it just doesn't work without wifi. Now they say it does and they VERIFIED IT.

Now, here's what minutes later ANOTHER AT&T representative wrote:

Rosendo - Supervisor: If applications such as Whatsapp were used, there will be no Long
Distance Charge as it will be taken as Cellular Data usage
Rosendo - Supervisor: Which means those calls went through regular calling
Rosendo - Supervisor: As that kind if error does not occur in our service
Rosendo - Supervisor: Only calls made through the pre-installed calling application of the
phone will be charged for Long Distance Calling
Rosendo - Supervisor: If third-party applications that use only data or Wifi to call, these
charges will not appear on your bill

So... basically it confirms everything that the previous agent said only completely the opposite, I got a sensation of walking on a mobius tape... the same conversation leads to one conclusion and then exactly to its opposite.

This is really confusing, and worst of all, expensive since they charge for the calls. Each agent has a justification for the charges even though both agents use opposite arguments.
Did I mentioned the fact that the phone user doesn't even know how to dial internationally?

To turn a confusion into a mystery is very easy, all I did was to ask the supervisor to confirm if the calls were made using an app or the regular phone system... and voila:

Rosendo - Supervisor: I apologize but as much as I would like to verify that, for security
purposes, we are unable to see what applications were used for your privacy as well

Well, that's what you got for talking to a supervisor!! At AT&T the supervisor has LESS power than a regular agent.... since Ken was able to VERIFY that the call was made using a 3rd party app, while the supervisor can't even check.

I wish they had the same system for the charges... charge you xx at the begining of the bill and then charge you the opposite (-xx) at the end.

Finally I asked for a phone or address I can contact to escalate the matter and... of course:

Rosendo - Supervisor: We do not have a mailing address for any specific department

In the end they got me a weird PO box.

So, in the end, we're been charged for calls we didn't make or maybe we made with whatsapp, which nobody can verify (for our safety) but that have been accurately verified as made using an app. We just have to pay, that's for sure.

Does anybody at the forum has a better alternative for contacting AT&T management or so? I found some TV stations (univisa, telemundo) have departments that like to investigate these matters but I would like to exhaust direct communication first.

Thanks