If your landline is provided by comcast, it also has a voicemail service, which you may have turned on.
To find out.
On your landline, dial your own phone number. It will usually ask for a pin number, but not always(you'll have to remember this pin or reset it). It will then connect you to Infininty/Comcast voice mail service. By following the prompts you can listen to, save and or delete all your voice mail messages and then turn off the voice mail feature from Comcast. (That assumes your own home phone has its own voicemail.