You are not the only one. It took me several months to take the serger out
of the box and use it. Take it to the shop and ask them to make it work right.
Maybe ask them to give you a demo. It might just be the threading. It's
very picky but once it's threaded, try not to unthread it ever. LOL. Just
kidding. I have rethreaded but I avoid it as much as possible because it's
such a pain.
When/if you change the cones, set all the tension to zero and pull the
threads very gently, then reset the tension back. Read the manual and
watch the videos. Once you've used it a few times you will get it.