When setting up an account in BIS, it likes to do it automatically by default. To get around the automatic detection, I would use the BIS website for VZW and put in a bad password for your account. It will try to connect for about a minute or so and then fail. It will then want you to try again and at that point there should be an option for you to manually configure the account. Since you know your settings, choose to set up your account manually. If your company's mail servers are accessible from the outside, a BB can connect to it, so please don't give up.
Verizon's BIS Website: https://bis.na.blackberry.com/html?brand=vzw