update: "available credit" still on the same level. It's been more than 10 days now. I don't understand what is going on.
They're notorious for that, not releasing CL even after payment has cleared. This happens even if you paid from a legit bank account. If you call them, they usually clear it manually but no idea how it would work with billpay, as the reason they cite for the hold is usually some BS about needing to verify payment is finalized.