Mobile error - You have too many devices paired with outlook

Hi,

One of my mobile admin mailbox is registered with 51 mobile devices and when he try to test one of the mobile device now he is getting below error. We are having Exchange 2013.

"You have too many devices paired with outlook. Please remove unused devices and try again"

I've collected all the identity of the devices and removed all the devices using below command.

Remove-ActiveSyncDevice –Identity "device identity"

But still all the devices are showing when i run "Get-ActiveSyncDevice -Mailbox user" command and still my mobile administrator unable to connect mailbox using mobile device and getting the same error.

Can you suggest how i can remove all the devices from user's mailbox successfully if more devices registered in the user's mailbox.

Thanks.