Vodacom data disappear.

I have a 20 gig wifi data contract with Vodacom for a year know and never run out of data. In February my data run out on the 8th of February and in March my data run out on the 5 March. Since the 5 March I try to get a report out of Vodacom to proof the usage for the data, with no luck. I know for a fact that it is impossible for me to use this amount of data in 5 or 8 days. I am not total clueless when it comes to technology as they think, and I am sure that there are something suspicious regarding this. If Vodacom is innocent, why don't they supply me with the information to clear their name.