Cox equipment return receipts can be complicated to read. Due to repeated reported issues with equipment return issues, I have all of my receipts framed on the wall for quick reference. Looking back at them, there's usually a table under the converter information section that has 3 colums: Serial# Item# and Issued. This list will include all equipment that was linked to your account at the time of the transaction. Returned equipment will indicate "RETURNED" for the Issued column and will list the date the equipment was issued if it still remains on your account unreturned.
I suggest checking your receipt again to make sure none of the equipment listed has dates shown in the Issued column as that would indicate it has not been returned.