Cannot delete old device

I have replaced a sensor but i am unable to remove the old sensor device. When i try to REMOVE device (i.e. remove the link associated with the old sensor and my alarm base station) it does not work. (get the message - "we had problems communicating with the device" - the device is broken). Because the device is still linked to the base station i need to override every time I set the alarm. I have tried to remove via app on my phone as well as via web page, but no success. ] Can anyone help? thanks