Vodacom Charges for Whatsapp Calls

Vodacom Charge me for Whatsapp Calls, Im overseas, My data was switch off on the 1st of July, So from the 2th of July I had only acces to the internet. I got a bill for Data Roaming and Voice roaming of over R 400 rand, When i ask vodacom they said that its because i use mobile data, I went to my phone and i check i havent used any data since 01 July 2019 at 20.00 at night, so where is vodacom getting this, the only thing i do diffrence on my phone is whatsapp call. so I have ask Vodacom for a report to indicate were are they getting this from. they submitted a report but this Doen's indicate where i use the data, so my conclusion is that Vodacom Charges for Whatsapp Calls overseas. Even if you are on WIFI, I have proof that Didnt used data from the 01st and Vodacom cant tell me Where is this data going.