So, I do think this is Credit One and that they're actually calling out to collect. Here is the voicemail they left: "All of our representatives are currently assisting other callers. Please continue to hold. Hello. Hi ___. Hello ---. Anyone in the line. Sorry not hearing any valid on the other line I'll be forced to disconnect the call." But, there are a ton of reports of this as a scam who demands you pay right away in what sounds like an outsourced, foreign call center. Just to be safe, I would not pay over the phone but say (if you do owe money) that youll do it online.
You might have paid your bill and they could be mistaken but I'm pretty sure its actually Credit One. I think they've had some issues with their customer support being very poor, however, so they might be treating you awfully.