The equipment return kit they send, as well as the return label with it, is tied to your cancellation, so sending your equipment back prior to cancellation is not at all advisable. Because it wouldn't come back with the proper documentation there's a very strong possibility that it would never get credited as you having sent it back, even if you included all pertinent account information.
An alternate phone number for cancellation is 877-329-1403. You may have better luck getting through, though you may still have to wait on hold. As with the main number, you may have better luck trying later at night.
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