Phishing Scam?

I just want to verify if [Edited: "Invalid Phone Number"] is a legitimate Comcast phone number AND that this dept does make calls on Sundays AND if not, is Comcast selling their customers information. 

My phone number is tied to an elderly family members account, while I have svc w/ ATT. Received a missed call this morning from that number. A vm was left stating it's about an important matter. Called number back later and immediately upon picking up, party on the other line asked for acct details. I responded with it's the same number that I'm calling from. I'm returning your phone call. I wanted to know what dept I had reached because in my yrs as a Comcast customer, have never received a phone call on a Sunday about anything. I wanted to verify if they were indeed Comcast or they were scammers. Silence on the other end for about 20 seconds. I asked if they were still there and the lady replied and I asked again what department did I reach. She finally answered and said billing. By that time I had pulled up my family members account and there was no past due balance. I asked her again what department was it, she said billing. I thanked her for her time and said obviously this is a scam because the account is not in past due status by any means. And just for giggles, I asked could she confirm or deny that she was truly with Comcast billing department, who makes calls on Sundays when at any other time it's like pulling good teeth to reach a live agent. Silence again.