Sipgate Incoming call issues

Hi folks,
Hoping that somebody can help me with the following:

I use sipgate and a Linksys PAP2T, I am based in Spain and use telefonica although I have a uk landline number. The linksys is wired to the router (standard telefonica one) with etehernet cable.

Outgoing calls are great, superb quality and reliable. Incoming is the same most of the time. However, regularly (Like evry day) it will stop recieving incoming calls, calling the number gets a message "you have dialled an incorrect number). Unplugging the router from the power and re powering it solves the problem but then after a few hours or a day it comes back.

Any ideas?

Thanks
Angus