Key is sending signal but car wont open other than manually

is the battery in the key ok, poss the reciever for the key signal is faulty, you need to get your local garage to carry out a diagnostic check on the alarm to pinpoint the problem

Could try resetting remote key ,


CITROEN XSARA—XANTIA—SYNERGIE– EVASION - Remote Key
Programming
CENTRAL DOOR LOCK (1 BUTTON PLIP KEY)
1. Ensure all doors are unlocked using the key.
2. Press and hold the plip key button until the LED stops flashing.
3. After releasing the button, the LED will light constantly.
4. Press the Plip Button once, and the LED will extinguish.
5. Open the door and hold the Plip key near the Ignition switch, and press the plip button once.
6. Now turn the ignition ON, and wait 10 seconds then turn ignition OFF.
7. After 5 seconds the Plip should now operate.


CENTRAL DOOR LOCK with DEADLOCKING (2 BUTTON PLIP KEY)
1. Ensure all the doors are unlocked using the key.
2. Press and HOLD the large plip key button while the LED flashes continuously for 20 seconds. After
20 seconds press the small deadlock button once while still holding the large button.
3. The LED will stop flashing.
4. Release the large button and the LED will light constantly.
5. Press the large button one time, and the LED will go out.
6. Open the door and hold the Plip key near the Ignition switch, and press the large plip button one
time.
7. Now turn the ignition ON, and wait 10 seconds then turn ignition OFF.
8. After 5 seconds the Plip should now operate.

Hope this helps .

ive changed the battery in my key remote but still nothing is happening, is there anything else i can try?