I think the better question is why do you think this is wrong?
I would guess that you are getting multiple rows back for each customer and therefore you think you have done something wrong. I would be willing to bet that you are getting a row for each billing cycle that a user has been through.
Well, as far as the naming conventions, it's not my db. I just sort of inherited the responsibility of getting the data out since I'm the only one who knows SQL at my company. Cut my teeth on RBase back in the late 1990's and i's now come back to haunt me!
The system returns no data when I run the query. I get a popup box that says Unexpected Error.