Carl,
What information have your received in addition to the new operational account number? Did you get the name of the customer? Or the address?
As Kivanc suggested, go to SE16N, enter KNA1, in field NAME1 give *part of name* and execute, maybe you get something.
This is no way a stupid question, I would say it is difficult question to answer because we are fishing in the dark 
. If you can, as members have suggested, ask the concerned person for the SAP customer number.
added: I too am hesitant to ask questions. And when I do muster the courage, the time to ask that question is gone 
But in an online forum, you can ask....
TW