Inbound route restrictions

Hi I’m a PBX newbie andI’m currentky updating our phone system right now. I need a help

How can i restrict a specific extension on the inbound route let say I have 1 server but i have 2 inbound route because of different company and department

Sample

Company 1.

Inbound route
714-255-0001
Extensions
601, 602, 603

Company 2.

Inbound route
714-255-0002
Extensions
701, 702, 703

If the customer calls the company “1” and used the “Direct dial” to dial extension 601 but unfortunately he/she accidentally dialed the extension 701 and the rep using that extension is definitely dont know the customer query because its a different company. I just want to know if that is possible to restrict the other extensions.

Thanks