seats not booked

hi I m Michael from Belgium, i made a booking 2 March Syney-stuttgart and return, no prob to go but then for my flights back I have an issue with the seat of the first and last plane and nobody replies!!! I just got an email 3 days before my flight so the 22 and i have to fly next Monday 25 april, can somebody tells me what can i do? Except calling, i m gonna spend heaps of money for a call