Error Code: 400--The namespace name is previously used in another project and has been deleted less than one week.

I am getting this error while creating Service Bus Namesapce using "New-AzureSBNamespace".

Error Code: 400--The namespace name is previously used in another project and has been deleted less than one week.

Can someone help me if there is still a fix for this bug.

Or is there a way to override this?? 

I don't know is ServiceBus allow underscore in its name?

Thanks!