Data disappear (3 Months in a row)

I get 2 GB data on the 1st of each month... For the last 3 months all my data dissapears and by the 4th I'm out of data. I had this contract for almost 2 years and never had an issue where my 2GB wasn't enough!!! I went into a vodacom store but no one could assist me. Phoned the call centre and they logged a call in September..... Still no response!! What the hell is going on???? There must be a mistake on their side. I monitored it this month to see if it could be a mistake but it definitely isn't!!! It is in-possible to use 2GB in 4 days without being on my tablet... I was on my tablet last night for about 10 minutes and thats it!! How on earth does this happen?? I want my data refunded to me!! I need this sorted out now!! I pay my contact fee's for nothing... I only go onto facebook and emails.... I don't ever download anything.... Please explain how this is possible??? Vodacom is getting away with disappearing data because we complain but nothing gets done about it!!! They just think you are lying about your internet usage!! This BS and should be taken higher up to someone that can actually solve the problem!!!