Missing Trade-In credit

Missing iPhone Trade-In Credit. I purchased a new phone in September and elected to trade in my old phone for the monthly credit.  Old phone was shippee back useing provided USPS lable but appears to be lost in transit.  I have opened a missing mail request with the USPS but since it was not my personal label there isn't much more i can do.  It has been 3 months with no monthly credit for the trade in and i'm not sure what else to do to resolve this.

I've tried multiple times with phone support to resolve this with no success, hoping you can help.

I have sent a DM as well with all relevent tracking and account info.