how can i fix my citroen picasso?

after driving for about 5 miles my gears stick, they wont change and I have to turn of the engine put it into 1st then restart the engine. There was a brake fluid leak which has been repaired by a garage and also the slave cylinder and head cylinder where replaced as it was still not going into gear. The car has now been in the garage for 8 days and they are saying they cannot find a fault. Ime at my wits end.