I use all the same and exact information, including email, name, address etc, to register in both 51test.com and mba.com. After I send out the additional score report request online, I wrote an email to gmat@ets.org to make sure ETS deal with my request correctly. Soon I received the confirmation email that ETS will send me the No.885000000017XXXX to the school I defined.
The processing is very quick, I send out online request on Jan. 19, got ETS confirmation email on Jan. 22, got school's feedback on Jan. 26, and received ETS formal copy letter on Feb. 3. So I definetly suggest to use this method to send out ETS score.
About your problem, I guess you may check like this way:
1. review whether your account in 51test.com and mba.com uses all the same and correct info.
2. you could check the problem by sending email to gmat@ets.org. ETS promises to give out feedback in 3 business days.
my experience is to call them. You feel safer and besides it's faster than any others. just keep calling for 30 min. you guys should be able to get through.