Hi, I'm Nathan.Sorry to hear that you're having trouble, but I'll do my best to help you. Please give me a few moments to review your details here.
Pick up your home phone line, and after you hear the dial tone key in *99, this will route you into the voicemail system.
If that doesn't work, after the tone key in your full 10 digit home phone number.
You may be prompted for a pin, if you don't have one or know what it is, you'll have to call comcast support to set one up or reset it.
Let me know if that works for you.