PCS Stamps & Coins  -  Unsolicited mail and attempt to send something I never ordered

Today in the mail I received a letter from PCS Stamps and Coins telling them would be shipping to me a Celebrating America coin collection. The letter stated I need do nothing and they would send the first of a series in a few weeks for $18.95 plus shipping. If I don't want it, I had to return a letter to them, they did not provide a return envelope or call a 1-888 number that is a lengthy voice mail asking for a lot of information I refuse to provide. No customer service rep was available. I did not order this item, I don't do business with this company, I did not ask for this item nor did I ever attempt to contact them. This appeared in my mailbox out of the blue! Now I am stuck trying to figure out a way to stop this before it turns into something of a headache. I sent them an email telling them to cease and desist and that I have NO intention of paying for anything I did not order or ask for. The auto response I got was that it takes 2-3 business days for them to respond. How dare they! Who do they think they are?