lukec233 (from 2014; sorry i wasn't around to see this), and
haryhanne (from this evening)-- welcome to Automotive Forums
(some way more tardy than others)..
hary; i hope luke already figured his out, but ibiza's do have a reset
for the door locks.. it is:
turn ignition on to POS 2 (red lights on dash)
turn ignition off immediately! and pull key out
While holding/depressing one of the buttons down (doesn't matter which), press the other button 3 times (with a slight pause) 1,---2,---3,--- ..
Watch the LED on the fob (it should flash) and the doors usually try lock/unlock.
and while unfamiliar with all SEATs, for my Audi and SAABs, the antenna assembly is
tucked under the trim panels of the back rear door frame..
i have opened up many an Audi and Saab, and unbundled their wire/antenna (which is usually just bunched up and zip tied directly near the receiver box) and tuft the 2-3ft of wiring, and run it up the pillar towards front of vehicle/sunroof; under edge of headliner.
this; i have noticed, increases remote activity to almost a football field (american; not futbol- rest of the world): 200yards/metres..
hope this helps..