You're talking about the iPhone 148 plan right? It's 3GB + 3GB. I'm using the same plan. First 3GB (Mobile Internet) is for your normal usage (browsing, Twitter, Instagram, etc). The other 3GB is solely for FaceTime, iMessage, iTunes, App Store.
Sorry for the many replies. Slow internet. Yeah mines new. With the new iPhone. I would say best to ask the Digi store in your plan. The link I posted shows the latest ones. I think released last year. Maybe they migrated yours to their new plans? Since its 148 as well