Guthy-Renker Endless Vitamins refuse to refund money Des Monies, Iowa

I had an order for the endless youth vitamins delivered to my home, I sent it back with the mail man aug 18 as refused as I have lost my job.  The company claims a month later they havent recieved the package back.  After calling and complaing enough they sent me a form to fill out telling me it was to state the I sent the package back and dont have it. 

I have sent it back and after a week they state they didnt receive the letter.  However I was told the day they receive the letter I would receive a refund for the item.  How do I get my money back as this company is a ripoff do not order from them if you want money your money stolen.