Q:

Can't delete Azure AD Tenant even though empty

When trying to delete my tenant I get this message:

However if I go to look at enterprise applications its completely empty, so can't delete any. What can I do to delete this?

A:

You need check with Get-AzureADServicePrincipal. Please ensure the cmdlet return null. 
If some application SPs are  in your directory, please use the following command to delete them.
Remove-AzureADServicePrincipal -objectid [enter object id here]

More information about this please refer to this blog.
If you have multiple service principal, you could use a loop delete them. Just a example.
$sps=Get-AzureADServicePrincipal
ForEach ($sp in $sps) {
    Remove-AzureADServicePrincipal -objectid $sp.objectid
}

