My domain results not registered.....but i have the invoice
 

I guess i got a problem:
I did an account in sedo.com to try to sell my domain (it is merely a try to look how sedo works). But when i tried to put my domain on auction section they told me that for them my domain has not been registered.
I checked on whois and it results already registered, I also have the invoice that attest i bought it (besides all e-mails with order confirmation and everything).
Now, that's what I said to sedo's staff and they asked me to send them the invoice that attest I am the owner.
what should i do ? can I have confidence sending them the invoice ? (I know this question could seem patetic but I'm not used to have confidence easily)
thx for any advise

Yes it would be safe to send them your invoice...

Usually if they ask me to prove I own a domain I simply point it to one of thier parked pages and then when they see I control it and its accepted I put the original page back.

did you buy it the same day you listed it for sale on sedo?

no, i bought in october 2010 and listed it for sale just 3 days ago.

you know I fear scam on these kind of things.