Am I being double billed?

That is typical of AT&T's convoluted billing system. Something similar happened when I ported my late mother's phone number to my cell phone (the number had been in the family since October 1959):

On 26 December 2015 I received my bill covering the date of the phone number change. It was DOUBLE my regular bill initially. I was finally able to puzzle out what AT&T did. OK, the old phone number was in effect for about the first six days of the billing cycle, then the new number was in effect for the remaining portion. So what does AT&T do? First they charge BOTH numbers the full billing cycle amount so it starts out being double. Then they list all the credits for the first 6 days the new number was not in effect. After that they list all the credits for the remaining portion the old number was not in use. Finally after two pages the final, TRUE amount due is listed which is close to a normal bill (allowing for the varying tax amounts each month).

Talk about a ridiculous way of doing things. All my other utility bills just use the date of a change to signify a change. The period before the date change is listed with the amount due for that period, then the post-change period amount is listed, and lastly the sum of the two sub-amounts. All this fits on one sheet of paper.

they charged me twice in November.  it's in black and white on my statement.  Yet, they claim I wasn't. 

@nonplussed

You can do as the OP did and redact personal info and post your bill.  We would be happy to look at it.  

Or it may help to look at the OPs sample:  Note the dates.  He is being billed for November - December, then for December - January.  This is a typical first bill, for past service and current service in one bill.  Future bills will reflect only one, current month.