Vodafone Used Up My 40 GB Internet Even Though I Did Not

While my phone was connected to Wi-Fi at home, my Vodafone internet suddenly dropped by 20 GB. I filed a complaint, and customer service said they would get back to me within 10 business days, but no one responded. It's disappointing that such a large company can't provide clear information about data usage. The same thing happened again today! I have a monthly data limit of 40 GB. Suspecting something was off, I tracked my usage with an independent app. Despite using only 23 GB, all 40 GB were gone. I even restarted my device and double-checked all settings, but nothing changed. Vodafone really needs to look into this issue and offer a proper explanation.