Hello Sasi,
if remote router serial interface status is down down.
This means remote DCE-3 is not receveing the CD signal and so DCD is down on the serial interface.
Have someone check the cabling from the serial interface to the DCE3 (if any).
Have someone resets the DCE3 box.
If still you have a problem you need to open a ticket with the WAN service provider
Hope to help
Giuseppe