RevG not sure why AA would contact you, as its run solely by Citroen Assist!!!!!!
It runs on an annual subscription basis and your dealer 'should' be able to renew for you (mine had no clue, so I did it direct through Citroen site - tried RAC, Green Flag, and AA and they cannot do this in UK).
It costs about £60 for basic cover and £80 if you want pucture repair (handy with no spare wheel), and fuel run out cover.
If you don't pay they say the SOS one will continue working but the assist will not - did'nt want to gamble so I paid up.
Interesting feature as I was unsure what happened , so pressed button when I got car - the SOS one goes through to 999 emergency services - they ask you what service you require, and once you start dialling you CANNOT stop call, they have to!!!
The assist button rings Citroen Assist pan Europe and can also send message from ECU fault diagnosis and GPS co-ordinates. How smart is that?!!