Return processing center

I have to return a mobile phone for which Xfinity is unable to generate a shipping label because their system cannot process returns when the 14-days return period expires. A Xfinity supervisor in the Customer Service department, who I spoke with, told me to ship the phone to Xfinity and gave me the following return address. 

[Edit: Address Removed]

As I was preparing the shipping package, I realized that the zipcode 73122 does not apply to Tennessee. So, I called customer service again and asked for the correct address. The agent refused, saying that it is confidential. He refused to help me further about how to return the phone. He refused to connect me with the supervisor who gave me the shipping address, in spite of telling him the name. 

So, I am here to get help about returning the phone. Can someone give the address of the Return Processing Center? Thanks.