Ownyourmodem Claimed I defrauded them, but took my money and still have the modem I returned to them -- who's the fraud? Orem Utah

I ordered the Arris TG862G/CT version modem based on pictures and the link to the official Comcast users guide on the seller's site. I received the earlier TG862G/TW. Furthermore, as per seller's detailed instructions, after completing the initial setup, establishing contact with Comcast, and initiating the update procedure through the Comcast website, all the lights on the front panel of the modem started to flash. This occurred through several reboot/reset cycles.

Since it appears the modem is defective, I asked the seller to cover the return shipping (since I did not receive the product I intended or the one inferred by the site and since the modem is defective) and replace the product with the more current TG862G/CT. The seller authorized return of the article with these instructions:"Per our return policy that was clicked and accepted at time of checkout, buyer is responsible for return shipping and if the unit is confirmed as defective then we may be able to compensate your return shipping costs. Please feel free to place a note in the package detailing your reason for return and your welcome to return the item to the return address below where it will be tested and handled accordingly:

Ownyourmodem

1577 N Main St.

Orem, UT 84057

I returned the modem via USPS Priority Mail on 25 Sep. I discarded the tracking number after it was listed as delivered by USPS. Now, through several e-mails, the seller refuses to process a refund or shipping cost reimbursement because I cannot provide a tracking number that I was not obligated to provide. Their last response:

"Please confirm any return tracking info showing this [return confirmation] and any error on our part and I am happy to look into any such accusation and get this resolved upon confirmation."

They have accused me of fraud because I cannot provide a tracking number and taken no action even though I returned the modem in good faith according to their own instructions. The seller refuses to even look for the modem in their own warehouse/office even though it was packed with an RMA and clear identification.

Thus, they have the modem they sold me, and have pocketed the $90 I paid for it.