You can use the console port to re-enable access to the router.

Connect your Computer serial port to the Vigor3300 console port.
Console port settings: baud rate 57600, 8 bits, no parity,1 stop bit

once you log into the router issue the following command:

system port -m 1 1

You will need issue the following reboot command to enable this setting:

System port -r

Configuration parameters for system port command are:
DrayTek> system port ?
Full Name:
Manage Port Function
You need to reboot to make changes took effect
port -s (Display manage port setting)
port -r (reboot to apply the changes)
port -m
port -e
port -p
port -i

0 : Default ; 1 : User Define
default: 80
default: 23
default: 22

0 : Disable all from Wan;
1 : Enable all from Wan;
2 : Enable only defined Wan IP;