Straight Talk Data Cap

I recently switched to Straight Talk (AT&T Micro Sim) and was getting consistent speeds of 6 megs down, 1 up but have noticed that my speeds have been around 200K for the past week and they won't go any higher than that. I called Straight Talk customer service and they told me that I had been throttled and that the cap was 1.5GB. I am under that cap and don't do anything other than downloading apps/updates and checking my various social media apps. They were unable to give me a clear answer as to why this happened, which is really frustrating. Anybody else have this problem?