This has happened to me repeatedly! It has caused me to increase my data plan intermittently to avoid overages when I was unable to access my account online. I called last fall (2016) and it stopped for a while. It has recurred again the past 3-4 months. I check my usage online and it isn't even close to the amount I was notified about!!
I chatted with a rep online 7/21/17 and she confirmed the data usage was as was shown on my account online and she assured me the matter would be resolved. Today, 7/25/17 I get an email that I now have only 25% data remaining!!! There is no change on my account data online from my review last week so I basically have no info!
I am going to search for another provider!!!