Why does 2G and 3G use my 5GB of 4G data?

Howdy,

I am wondering why when I am in an area that only has access to 2G or 3G speeds that

my allotment of 5GB at 4G is used?

Called 611 tech support today and they said that this was the case, but no place in any of

the TSA or EULA does it state that this is true.

So I am wondering Why is my 4G allotment of Data used Up when I am NOT connected to 4G?

I have a Nexus 5 which is 4G LTE capable.

thanks for the info in advance....