I sure hope that your account is paid by CC. If so, then write a letter to your CC company disputing the charge. Calling does not protect your rights. You must write a dispute letter. Since D* has already admitted to receiving your package, they cannot defend the charge for non-return of equipment.
Didn't the phone companies learn about material changes to contracts voiding the ETF's? Perhaps D* (and E*) should be looking at what is happening in the phone business when they change their contracts (and fees) and thus voiding parts of their contracts (the ETF's).