Phantom Data Charges!?!

For years my wife has used ~70-120 mb/month on her iphone. So a few months ago we switched her data plan over to the 200 mb/month. Now in 3 of the last four months she has gone over.
Each month there have been incidents of single data transfers of 50-150+ mbs. I am convinced these are all phantom charges. Obviously this causes her to exceed her limit quite quickly. The first 2 times it happened I was able to reason with people have the overage charges removed.
But now this has happened again with a new phantom transfer happening each day around the same time (9pm) ranging from 5mbs to 110mbs over the last few days. The best part is most of the times these have happened she's been at home on the wifi network.
Anyone else have any similar issues with AT&T?