Same name

how can be possible there site can register same name

i have my site 3 same name like abbiejoe520, abbiejoe520 (2), abbiejoe520 (3) abbiejoe520 (4)

how that can be possible and where i can change that not can be register same name?

I'm sorry, but can you explain your problem more clearly? Are you talking about usernames, or...?

Make sure that email address is set as a unique field.

Sorry,  yes i mean username

You must have accidentally unchecked the unique option in the field's preferences. Navigate to Administration > Builders > Profile Fields and check the unique option for the NickName profile field.

You'll most likely have to delete the duplicate members, or change their usernames to something else.

Thank You :)