My name is ***** ***** I will be assisting you with this question.
There is indeed a company called RTA Business Consultants, Ltd, registered with Companies House and located in Stockport at postal code SK4 5BH. They incorporated in the UK on August 21, 1972, and have been in business for a long time. Companies House says they are an active corporation and they are up to date with all of their business and tax filings. You can go to Companies House's site, look them up on their register and see all they have on this business. They are company #01066879.
All of that said, there are many complaints about RTA for unethical or illegal practices of one kind or another. If you haven't yet discovered this for yourself, you can find links to many of them here.
So are they legitimate? In the sense of actual, yes. Are you likely to be pleased in your business dealings with them? Impossible to say. A lot of people aren't and if your situation is like theirs, you likely wont be satisfied with them either.
Are you saying that you canceled your check to RTA?
If so, in general it's not a criminal offense to cancel a check except if you wrote it in the first place to get services you didn't want to pay for with the intention of cancelling it, or if you wrote it against funds you knew you didn't have.
In particular, RTA will likely want to come after you for their money, since nothing you have said indicates that they did anything to breach their contract with you. But this area is really a different question from what we started with and should be addressed separately, not to a US fraud examiner and criminal lawyer (me) but to a UK solicitor.
I can just confirm that RTA is an actual company doing business but apparently under the gun for shoddy practices.
If you're interested in discussing your legal rights, you need to open up a brand new question in the UK law category and ask one of the site's verified barristers or solicitors. While I'm willing to call the UK, there's no point in my doing so if it's something that you specifically need to discuss with someone licensed to practice law in the UK.
If there is something more about the scam aspect that you want me to address, please reply here and let me know what it is.
Just checking in to see if you need more help or any clarification of my answer. If so, please reply here on this question thread.