[chill1]

> ".. Twilio usage that resulted in a billing transaction (e.g. 1 cent for a SMS message or a phone call) triggered the billing system to attempt a recharge using the credit card associated with the customer’s account. This only affected accounts with auto-recharge enabled."

> "Consequently, the billing system charged customer credit cards to increase account balances without being able to update the balances themselves. This root cause produced the billing incident of customer credit cards being charged repeatedly."

Sounds like when an action required funds from a user's balance (which their system thought was 0), it attempted to recharge their balance by charging their credit card. And since the system also could not write to the database (to increase the balance) the balance remained at 0. Thus, the system kept thinking it had to recharge the balance again.