My car ?

My engine auto diagnosis light came on and 3 min later the car stop call the AA done this and that and he done something 2 the battery the lights were ok till he mess about with them now the battery light stays on got the car to a repair shop last week now they say can't fine out what it is and could cost 1500 to 2000 pounds 2 fix they say all the lights are not working would that be to do with the battery light been on all the time for the last week can any 1 help .the car is a Citroen C3 LX