The short answer is if you already submitted the work that you purchased, don't pursue the refund and don't publish their name or do anything to antagonize them into being vindictive. Move on, learn from your mistake, and next time, just use this forum to find a legitimate writer. If you never submitted anything that you purchased, post the name of the company right here, ignore their threats, and pursue the refund through PayPal or your credit card company. If they actually try to follow through by contacting your school, you have all of the chats and/or emails showing that you tried to cancel the order and your (truthful) position is that you were going to order a model essay to help you fix your essay, but you never submitted anything purchased from anybody. They may give you dirty looks and warn you about not writing your own essays, but there's no actual violation for them to pursue against you.
The first website I found looked great - and the online chat seemed helpful.
And as soon as I started requesting the money back the phone calls and messages has started... They started threatening me and basically said that they will inform my university of my misconduct etc....
This is extremely typical: They're as cheerful and as helpful-sounding as they could possibly be until they have your money. It's all an act. As soon as you have any kind of problem with their work (or simply change your mind right after payment), you'll immediately see their true colors. They also make things difficult for legitimate writers because some of the best of us tend to be a little (or a lot) less patient about holding the hands of new prospective clients. Some clients end up choosing the friendly-sounding rip-off artists after contacting us, based mainly on their phony friendliness act and on their too-good-to-be-true prices. Those of us who actually provide a high-quality product and charge fairly for that quality are usually way too busy for hand-holding and/or for responding patiently to questions already very clearly answered in our FAQs (for one example of how this dynamic typically comes up). I know for a fact that some of my current clients tried out some of those places after contacting both of us, initially, before they decided to start using me, instead.
My question is - is there any truth to their claims?
But they do have my original paper that I still have to resubmit. Can I continue working on it?
If you wrote the original essay, you can totally ignore their threats. There's no such thing as "attempted" plagiarism and you haven't violated any university honor code by ordering a model essay that you haven't ever actually submitted for a grade. If this is the situation, you should immediately post the name of the company here for the benefit of everybody else who wants to avoid getting scammed and/or blackmailed by fraudulent companies.
I am gong to speak to Student Union tomorrow but has anyone been in a similar situation? any advice?
This is a mistake without any possible benefit to you. Don't do it. Your fellow students don't really know anything more than you do about this and those who might definitely aren't ever going to admit that in a Student-Union forum. Meanwhile, you'd be divulging things about yourself to relative (or total) strangers at your school for absolutely no good reason.