Find the name and address of each collection agency calling you. You can either get this from the letter the agency first sent when trying to collect on the debt, or by asking the person you speak with on the phone.
Type a cease and desist letter. Include your name, address and the date at the top of the letter. In the body, write a short paragraph demanding that the debt collector stop contacting you in any way about this debt. Mention the Fair Debt Collection Practices Act somewhere in the letter. State that you know your rights and will take legal action if the collector contacts you after receiving your letter.
Print out one copy of the letter for each collection agency that is contacting you.
Mail a letter to each agency by certified mail. This way you will be able to prove that the company received the letter in case you have to pursue legal action.