Return Issue

On November 12th I returned an iPhone Pro in the box that was provided to USPS. I have been trying to track the package to make sure it was returned on time in order for me to upgrade to the iPhone I actually wanted to get, the iPhone 12proMax. Thus far, the tracking site shows that it is still in transit to the facility, wherever that may be. It has been 15 days now and I know it shouldn't  have taken this long for the warehouse to receive it. Do I have to wait for the warehouse to say that the returned iPhone was received in order to avoid any holdups in ordering the phone I wanted? I certainly don't want to get charged for the returned phone and would like to take advantage of the upgrade promotion that is currently in effect. Any help would be appreciated.