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


Company 1.

Inbound route
601, 602, 603

Company 2.

Inbound route
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.