ok here is what you do
plug one servo into the reciever see if it works, then plug the other servo into the reciever, see if it works.

then plug one extension into a servo and plug the extension into the reciever, see if it works, repete for the other extension

if they both work
plug the y harnes into the reciever then plug the servos into the y harness, if only one works you have a bad y harness. it doesnt matter if you have 3 y harnesses...they are all bad

or just learn to solder and make your own extensions and this wouldnt be a problem.(just google it)