Have you compared the details of your bills to see the differences? I'm guessing it may be changes in your taxes/surcharges, which can change quarterly. Details about those changes are usually toward the end of your bill statement.
Why does my cell phone bill keep going up?
I was promised my bill would be at $120 and it was for a few months and now it’s $126 why is that?
Go to a mechanic without a car then make noises. They won't know what the problem is, same here. We can't see your bill, you know.
Look at your two bills side by side. Beats waiting 30+ minutes to have a rep do the exact same thing.