...

(b) ensure that my policy was not canceled, and
(c) bring my account balance back to zero

The rep unhelpfully repeated that I had overpaid by $5.00, causing my billing problems.

After much more back and forth, I discovered that Anthem had canceled autopay on my account, meaning that my August premium had, in fact, NOT been paid.

After much more unhelpful back and forth, I paid the outstanding premium by credit card.

In the mean time, Anthem's SSL cert had been updated...