How do you deal with an incorrect bill / collection agency?

The only way to make "noise" is to show your receipt that states you returned the box (which you don't have). The cable company has a contract that you signed that states you received a box and the fee if it is not returned. The only thing you can do is learn from this experience...ALWAYS get a receipt, NEVER leave anything for someone to "pick-up". When in doubt send it via UPS, Fed-Ex, USPS, insured, and "return receipt"...someone at address has to sign for the item and then you have proof. With UPS if you insure the item for $1000.00, the clerk has to open the carton and verify that the item is what you claim it is (well worth the $10 to $20). Even better is to return it directly to the customer service office and get a receipt (and save them for 10 years)...sorry for the bad news, but it's your word against their contract. Written contracts will always prevail over verbal.