Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, bear with us; re-confirm and post back with the complete model number of the home phone system. Additionally, who is your phone service provider please?
Have you tried bringing this to the attention of AT&T? It would appear that for some reason, the CALL FORWARDING feature has been enabled towards your "...google voice ..."