corporate controllers unit trying to receive an annual fee of $225.00 as a government agency and they are not denver, Colorado

Received a form letter requesting $225.00 to file your corporation (which we are not) with the State of Colorado.  There is no phone number, no physical address just a PO Box in Denver. The form uses words like "noncompliant" and "delinquent".  It also states on the bottom that this is not a government agency and it is not a bill but a 'solicitation' (basically for your money).  BEWARE of this letter that comes to you in the mail with a return envelope to send your money.  You get nothing for this!  If you file with the State the fee (that is legal) is only $10.00.
For the surrounding area of Denver, Colorado