Since the late night 11-11 we cannot connect to VPN anymore through our router.
As Brendan already pointed out, it could be a problem with the DNS. You can use a website based outside china to resolve the DNS then use the IP address to connect. Try:
If this doesn’t work then see if your VPN provider offers a different protocol. It could be that GRE is being blocked, or mismanaged on your router after a firmware update, this would affect PPTP which is the most commonly used protocol. See if your provider offers L2TP over IPSec, assuming you aren’t already using it – IPSec is used by cisco for their corporate VPN products, so is a better bet in general anyway.