Where is my data?

Am writing this with a heavy heart. So last Friday, the 1st of December I received my 5G for my WiFi at home, as per normal. Later the next day when I check, am already under 500MB. I have never exhausted my WiFi data like this before. I seldom download and I stream normally, also careful with my apps on our phones. Yesterday I called Vodacom and spoke to Kagiso who was kind enough to log into on the system with reference number 1- ********** ********** and said they will get back to me with 24hrs, am still waiting. I need someone to make me understand by explaining to me what happened to the rest of my data. Today am left with 261MB data, after a mere 4 days. This is really unbelievable hence I need someone to explain how is this possible. Your assistance will be highly appreciated.