cannot unregister/re-register device in onesecurity area, because of incorrect handling

I have a registered device (USG40) in my onsecurity area recovered from a partner that give me full authorizations. Registration went well but the device is hided (occasionally compair in some combo list...). If I try a new registration i get "already registered device" message. I got other device registration from same partner without problems. But in this case i don't know how resolve. How is possible unregister a device, or re-register?