I don't understand what is wrong in my command; unless it is the system ?
It looks like your command is
/tp @a [x=-3,y=1,z=0,dx=-9,dy=7,dz=0] ~ ~ ~-1
I see one error with this: you need to have the
/tp @a[x=-12,y=1,z=0,dx=9,dy=7,dz=0] ~ ~ ~-1