Re-Activating My Account for Billing Update

I am owed $72 by Xfinity for a refund for having paid in full for only a partial service for the month. For reasons outside of my control, my bank cannot accept the refund, and I need to change the payment method on my account. Because my account is now "unactive," I am unable to change any of the billing settings.

An official Xfinity ticket was submitted, and I received 0 help. It was immediately closed with the response "We are unable to refund your account." How can I reactivate my account so that I can change my billing settings?