Reading Club of America / I keep receiving bills

Many months back I lost my credit cards, since then I keep getting phone calls, and letters saying I owe$359... Now, and a total of $843.75... How do I get these people off my back. My credit is good. I pay all my bills ontime. i didnt order this readers of America club. I did notice one of my cards was being charge. Of course i canceled all of my cards. Now its phone calls everyday, What should I do. Please help.