I was having major data issues where my phone was downloading data anytime it was on cellular. Went to the apple store and had them swap my phone, then tested it out and every time I would open data usage it would show data being downloaded. I told the genius and he gave me a new SIM card and no more problems! I'm so excited since I've just been using my phone without cellular data turned on for the past week. If your having these issues I would definitely look into getting a new SIM card.