How can I get confirmation number for the GRE score sending?

I will take GRE general test this weekend, and I intend to use the online Additional Score Report service to send my score directly.
But this service require me the Confirmation Number, still the ETS phone score service also require this Confirmation Number. And now I know this number will be seen on my score report.
So, How can I know my Confirmation Number before I receive the report.
It is so weird that phone score service still require the confirmation number written on the score report, if one have receive his score report, need he call phone???

These are questions you should be asking ETS…