The very likely explanation, based on these calls not showing up when you examined your Charter account, is that this is unrelated to your recent Google Voice experiment. Most likely, someone is spoofing your Charter phone number to make spam calls.
Did the other person tell you whether these were legitimate callers, or if they were the typical junk robocalls?
If the calls are junk, and you don't see them on your Charter account, then it's number spoofing, which is rampant. Just in the past 24 hours, I got three of them on my Callcentric numbers. One was spoofing a private/consumer's number, one was spoofing a breast cancer hotline, and another was spoofing some random company. It's a plague.