Citroen C4 gear box

Hi my car is stuck in park and engine wont start even when pushing brake pedal down it wont start or release gear leaver brake lights dont come on when pedal pressed and a little line shows on display not the P for park if you jump the car from battery to starter it starts but gear box still locked if you push down switch under gear lever you can release from park and put into drive and the car will drive but only in one gear dont know what one as only a line shows on display you can also reverse but again only line in display ive had AA out and they checked brake pedal switch and said it is ok it is showing pending fault code u0103 it did not brake down while driving ? Any help will be apreciated thank you