Do I need an attorney if the company is threatening to press charges?

I received a letter from a Company that states they are representing a business. I wrote a check that was returned and on the letterhead, it has the companies name District Check Division I, but the envelope has another company as the company name. They sent a copy of a check that was supposedly returned 6 years ago. They did not copy the back of it, only the front, I never received anything 6 years ago from the business that I wrote the check to saying that the check was returned, as a matter of fact this is the first thing I have received, and it says it is the last notice they are sending me before charges will be filed and I will either go to prison or have to pay a fine, or both. What are my rights on this since this is the first thing I have received and I cant seem to find any information on this company?