Hi
with reference to my earlier post
Customer master are created at three level. 1. general data (which is created at client level / valid for all the company codes) 2. company code data 3. sales org level
If you forget to put the company code than system would have created only general data since you are able to see the customer in transaction code FD02 and not created customer using XD01 .
you will be able to see the switch tab only for general data on the top of the screen FD02. You will not be able to company code data.
again go to XD01 and input the same customer number and company code and create the master. it will create at company code level. You need to fear to go ahead because system wont create two master data with same number. but before that check the customer have been assigned to external number range or it is not possible to extend to company code level with the same customer number