If you want to limit what issue types a certain person/user can see you can do this in the "Project" --> "Settings" --> "Issue Types" by changing the "Group access" for the issue type to not include the person's user group.
If you want to give access to some issue types for some customer company users and not to others, then you can create different user groups for them.
- Create one user group called "A Customers" and another "B customers"
- Set the user groups on the users for the different customers to the groups above.
- Change "Group access" on the "Project" --> "Settings" --> "Issue Types" to reflect what users should see what.