Last month's data didn't carry over!

Me and my gf purchased the Pay-once 24GB data promo in the beginning of the year. So every month we get 2GB of data. Before I brought the bundle I have asked vodacom that any leftover data for that month will be carried over for next one month ie. so every 2GB will expired in 2 months. It has been fine up until last month, when I have built up 4GB for last month. I have used just over 2GB last month. And I noticed in the beginning of the month that last month's left over didn't carry over to this month. So I thought it was a system glitch and it will sort itself out. Now yesterday when my android notify me I have used 2GB for this month I went to check how many data I have left. And to my surprise the data didn't carry over. Then i asked my gf and she also didn't have her data carry over.

So now my questions:
1. Has anyone here experience this?
2. What should I do?
3. Is there any vodacom representative here that can help me?

Thanks