Verizon iPad data warnings

We have multiple iPads on post-paid 5GB data plans in our business account with Verizon. They're a mixture of 3rd and 4th generation iPads as well as a few mini's. Almost all of them at some point have shown the following message: "Cellular Data Plan Usage - There is no data remaining on your current plan. Would you like to add more data now? If you don't add now, you can do it later in settings." The user will call or email me and I'll check their line and they always have plenty of data left for the cycle. I've called Verizon and they just tell me to power cycle the iPads which does clear the message but it will come back at some point. Since this is Verizon's only response when I've called about it, is there any way to get this cleared up for good that they possibly don't know of? Thanks.