how on earth did you find that out while searching for the obd port?
but the real question is what was it doing unplugged? as above there should be only one socket for it to fit in but to get to it may be tricky. not sure if its accessible from the drivers side. if your flexible enough, remove the plastic panel underneath and go up the back of the glove box.
?? Do all MK3 Cupra have the CD Changer cable in the car then??
all should have a cable, but not always a changer