i need to change my lock on my upvc doors but the keys have been lost?

i need to change my lock on my upvc doors but the keys have been lost, the doors are in the locked possition and i can't turn the barral the 1/4 turn to dram the old lock out. i have tryed to drill the lock but my bit keeps breaking. the lock needs changed to secure the house as i have been able to open the doors with gentle force. how can i get the barral out to change it with a new one??