Vodacom data ****

I have been a loyal Vodacom client for many many years now. But as of the last year or so I have noticed my data usage becoming increasingly high. I have complained before and been repaid some money although they never actually admitted they were wrong. Lately my data usage has been so high using 2.2gigs for an 1.5 hour Skype call. According to skype it should use 30mb per 15 mins. So this doesn't add up. I have complained and have just been sent my usage report which confirms this but have had no response at all to my problem. The service has been shocking. I even tested a wifi zone usage while watching a video then the same in 3G and the usage on Vodacom was three times what was used on wifi. Apart from insanely high data prices already, now they are miscalculating how we are charged it seems. And the customer service has been absolutely dismal. With no actual explanation or attempt at one. Vodacom this is a big problem and I hear a lot of people complaining. Please can someone with technical knowledge explain this to me??? I have asked for many call backs and even asked to speak to a manager with no reply.