Broadband device unlimited data plan

Is there any grandfathering of the old Data Connect Unlimited plans on broadband devices? I'm not talking about data plans on smart phones, only the broadband devices? My plan says data is unlimited, but once I reach 5 gb it will not connect anymore. The plan on my bill lists the acccount as DataConnect 5GB, but then says "Unlimited Domestic Plan", and under My Account says "My data plan: Unlimited"; but like I said, once I reach 5 GB useage they disconnect me. From a quick online chat with one of the AT&T support people, they said that my broadband device plan expired in 2012, but I never received any notice of that, and if so, why does my plan still say unlimited??