I experienced the same problem. I was on $200MB/month data plan. I am mostly on WiFi and usually use ~5MB cellular data per day.
When I checked it yesterday, my data usage was at ~15MB. Then I received an email from AT&T that I was over my limit-- didn't receive any warnings! I am now 88Mb over my limit, which means I used ~270MB in a single afternoon.
When I checked it yesterday, my data usage was at ~15MB. Then I received an email from AT&T that I was over my limit-- didn't receive any warnings! I am now 88Mb over my limit, which means I used ~270MB in a single afternoon.