obvious thing is trace see what you send to the carrier, if you think it is in the correct format then open a case with your carrier.
There are a few reasons that the main site number is shown usually the carrier doesn't like the number you are sending it (incorrect digit format or TON etc.) so it replaces the number, or it can be a charged service to display the individual CLID and if your not paying they display the Main number, or just an issue in the carrier. All ways round if you are happy with what you are sending open a ticket with the carrier.