online advertise collection

We never advertising with yellow pages online or any online company. We are surprise when receive a statement from A.C.A Recovery ask to respond in 30 days. Total bill is $624.99, they did contact us couple times since we receive the statement (not very friendly), contact name Mr. Cutler 800-356-3713. We are not respond to them because we did not known this service or ever sign up for this services. How are we go about block them from calling us or send us bill in the future? We also find out today on the internet they are send out letter similar to the letter they send to us to many small company around the country. This is scary how are they legally scam people and still in the business. Need help and Hope to heard from you.
Kim Doan

Kim Doan