We regret to see your problem as a co-seller on eBay.
Strange to see why any of the eBay support could not give Proper/No cause for your listing problem.
Hope you can see the Account page -> seller dashboard and see for any notices of compliance.
Do you have any other account on eBay, if so, you may need to verify that account's dashboard too and resolve if issues of compliance exists.
Now, you should be calling your Account Manager, eBay. You can get his contact from your past mails or by calling 18002093229.
Hope your issue gets resolved soon.
Regards