xfinity mobile data usage does not add up

Hi, I noticed a few months ago, my data usage shot up, averaging about 3 gigs usage per month. My billing cycle starts on the 22nd of the month so I began reseting statistics for cellular data usage at 12am on the 22nd. Xfinity is currently reporting my data usage at 1.05GB. However, my iPhone is reporting my cellular data usage as 620MB. 

I have called Xfinity mobile twice to get to the bottom of this discrepancy. The first call took 35 minutes to convince the agent that I didn't want help lowering my data usage on my phone. He finally relented and said that he would be opening a ticket to investigate the variance of data reported by my phone and Xfinity's billing process. I was told it would take three days and that I would receive an email notifying me of the outcome. A week later and I've not received any email regarding this investigation. I called back yesterday, Friday, July 9th. This time it took 50 minutes for me to get frustrated enough to hang up. I believe the lady was trying to help me, I just don't believe she had the support on her end to get it done.

I would also like to point out that the terrible connection quality and lag to this call center does not help matters. That, combined with the heavy accents and broken english make this type of support call almost impossible.

Can someone tell me how I can escalate this issue so that I can get this simple question answered clearly and definitively? Preferably without having to spend another wasted hour on the phone with someone who doesn't understand my question.  

Thank you.