Outrages Data Charges

Received a R3298 bill last month with data charges of R1662.98 after having bought additional data again. Data seems to just disappear into thin air even when phone is not in use. Went and check the last few bills same story every month additional charges of at least R500 even after buying extra bundles. When calling Vodacom they cant explain and refuse to refund. This is ridiculous. Where are these charges coming from where is my data going. Should i just move to Cell C after being a customer for 20 years??? This is also not my first complaint.