Data bundle expired

I have a 5Gig data bundle, but ran out of data on 22 Dec. I then bought another 5Gig same day.<br> At the end of Dec, I received my monthly 5Gig as well, so now I have 10Gig.<br> All of a sudden on 21st January, I have no data, after having used only 8Gig. I phoned Vodacom, the lady told me that when I received my 5Gig at the end of the month, the counter \switched over"to use the monthly data"