Data usage

Iv had the worst experience with whom I thought was my trusted service provider, Vodacom. My data had gradually being used to the extreme over the past few weeks. I went to Istore to check with a technician to make sure my phone was correct, and still even though Iv been doing the exact same thing on my phone for the past few months my data was disappearing. I was told by the istore technician to contact my service provider, which I did today and had the worst service ever. I was told a technician would assist me by Monday, but I loaded 1gig data yesterday which is almost depleted today. So I would need to load another 2 gigs just to get to Monday for assistance? I was then contacted by Judith who is some sort of manager, of which she argued with me that my SIM card was used in another phone. Not possible! Even though I told her Iv been using the same phone for the past 2years and another iPhone before then, she still continued to argue with me. Which means everything else which she is going to say to me is null and void becos her info is incorrect! Pathetic service provider! Will definitely be changing in the new year.