Hello Kassayeb,
Welcome to the community!
Sorry to hear your bill is higher than expected. I understand your bill was attributed to call made to the Netherlands. I also understand the call was made via WhatsApp. I further understand you were told the the app sometimes uses cellular data. However, were the additional charges on your bill for long-distance or additional data usage?
In general, calling apps (ie WhatsApp, Viber, etc) use data to transmit calls. If a device is connected to Wifi, that data would transmit via the Wifi connection. If the device is not connected to Wifi, that data can transmit as cellular data.
However, unless you've exceeded your monthly allotment of data, I don't believe that is the reason for your additional charges. I suspect the additional charges were for long-distance. Unfortunately, there appears to be a bug with WhatsApp. While it's not mentioned on their website, it seems as though the app will automatically switch to using mobile airtime minutes (within the app) if it deems the internet connection is insufficient for voice calls. It has happened to many people across Countries and even Continents (see here). One suggestion to prevent the switch would be to enable Airplane or Flight mode and manually enabling Wifi prior to making the call(s). Doing so should prevent the app from switching to mobile minutes if the Wifi internet connection is not sufficient. However, it also means that you wouldn't be able to make WhatsApp calls using a mobile data connection.
As mentioned in my other post, mobile providers only know usage. They cannot divert calls from within apps to cellular calls. They have no control over how apps work. The mobile providers do not decide which calls go over their networks or how they transmit. That determination is made by the phone. With an adequate internet connection, WhatsApp calls are usually sent as data via the internet. On the other hand, if the internet connection is not sufficient, WhatsApp apparently switches to mobile airtime minutes. The mobile providers merely connect calls which the phone request to be made. If WhatsApp makes a call using data, the providers will transmit data; if WhatsApp makes the call using cellular networks, the providers will transmit it as a call over the cellular networks. If that call is to a number abroad, long-distance charges would apply. Unfortunately, in your case, it appears as though WhatsApp made the call over the cellular networks. Not connecting to the networks (ie Airplane or Flight mode) should prevent that from happening in the future.
You should note that these forums are community-driven and not intended as a venue for customer services. If you wanted to further discuss your issue, you would need to contact customer service again. In addition, they can also be contacted via Live Chat, Facebook, or Twitter. Those methods can be accessed via the contact page posted above.
Hope this helps 😀
Cheers
