If you select the correct line from the drop-down box at the top of vPanel, you can then select which number you want to use for that line's caller ID.

I have two different numbers using the same ATA, and this is exactly how I've done it, and each line shows the correct caller ID number on an outbound call.

If you have further difficulties, I'd suggest that you contact support and have them guide you through the change.

Good luck!