Username not available

I signed in using my gmail after some time not using zoho. On the next page i was told that this is my first login and i need to peek a username. I would like my username to be "meedummy", but i was told that this wasn't available. So i have peeked up another one. But now, if i search zoho contacts for "meedummy" system tells me it isn't valid. So why wasn't it available during my signup?