Lost my phone. Xfinity does not want to deal with it

I traded in my phone on a promotion that would give me $1,000 credits towards a new phone. When I received the new phone I proceeded to use the provided shipping label to mail back my old phone. I sent the phone around October 20th. I took it into the USPS Post Office and had it scanned in. The item has shown that it's in transit since the 23rd of October. Now Xfinity wants to start charging me for the missing phone. Xfinity did not put insurance on the phone. And USPS has communicated that the phone is lost. It is now December 6th 2024 and there still is no resolution and XFinity still wants to charge me for the lost phone. If I had purchased a shipping label I would have put insurance on the phone for just this scenario. But Xfinity to responsibility by giving me the shipping label. Why is this my fault. I followed all the steps necessary to send the old phone to them. Xfinity service is not worth the headache that they create. We have to call in at least once a month to fix something with billing. Issues with our service or a variety of other issues. [Edited: "Solicitation"]