That 600GB for R399 WiFi contract is a ****✋🏾

I have vodacom WiFi, 36 months contract. My contract was supposed to be R399 for 600gb😳😳 but now they deduct R434.78 and the worst part? That 600gb magically finishes before the month end but there are only 3 devices connected. When I first had the WiFi i had a full house and the WiFi worked well. Now it’s messed up! I don’t even know where to begin😭😭 it refuses to connect to other devices. I have called vodacom and they weren’t able to help me. I regret taking this contract everyday. It’s just me and my sister (2 phones and a tv) how can 600gb not last 30 days?