AT&T Cellular Data Usage Message! Urgent

My billing cycle reset on April 20th at midnight, so my current data billing cycle is from April 21st - May 20th.

I have an iPhone 5 with the 3GB data plan and unlimited Wi-Fi. I also have an app that monitors my data usage very accurately. I have not used any data except iMessages to my girlfriend and maybe two minutes max on Facebook. About ten minutes ago, I just received a text message from AT&T saying that I've reached 65% of my billing cycle. However, my data apps says that I've only used 0.7% of my allotted amount of data.

Is this an accidental mistake by AT&T or should I be seriously concerned about this?

Why did this happen?

You should be seriously concern anout it