Extremely high data usage Vodacom ! R40k bill

Hi, I am hit with an extremely high data bill of R40.000 for mobile data use while roaming in Mauritius. This happened to me with mobile data switched off and only being on the island for less than 3 days, after the 2nd day I received the soft lock message from Vodacom. I had mobile data on for maybe 5 min max and only to send a WhatsApp message without any pictures/videos. I also know my apps are not automatically updated (unless on Wifi) and I have been in a wifi resort all the time. I am getting nowhere with Vodacom Support and after a week (and already back in SA) there is no resolution. For a fact I know this is not right because according to mobile data charges for roaming, I should have used more than 40G of mobile data in about 48 hours ! What I also don't understand and what Vodacom cannot answer for me, is that I put a R5000 deposit down when I signed for my contract a few years ago to accommodate for international roaming so why did Vodacom only locked me when the bill was already R40000 ?