System is a KX-TD1232 with a TVS100 VM

Company A has three CO lines that are managed by AA on ext 165 company B has one CO line managed by AA on ext 166. DIL 1:1 Day/Night for Company A are set to ext 165 and company B is set in the same manner but to 166. Sometimes an incoming call for company A is sent to company B’s VM ext (166) this is very bad because they are two different companies with different company greetings/menu etc. My question is what on earth is causing this? and how do I fix it?