Tried that a few days ago, they gave me another number to call who didn't want to help.
I am anyway concerned that the 135 section tyre is too "thin" for the 5j X6 wheel as it is outside its approved maximum width range .
A 125/70 tyre is simply far too "thin" for the X6 wheel and should absolutely not be recommended as even relatively low lateral loads may pull the bead away from the tyre rim and cause rapid deflation.
A 145/70 tyre is the smallest permitted tyre size that can be stretched onto a 5J X6 wheel...so it should be either that or find a thinner compatible wheel to take the 135/70 or 125/70 space saver tyre.
Edit: Looks like even the 145/70 is not really wide enough for a 5j rim as it is normally limited to a 4.5j rim.