How do I escalate a missing iPhone trade-in issue with Apple?

I traded in my old iPhone via the apple trade in facility uk.appletradein. The phone was sent tracked via Post Office 10/10/25 and they eventually confirmed receipt 22/10/25. Communication has been very poor and I must have sent several email and always get the run around. The last email suggested they could not find it in their warehouse. There is always some excuse; not my problem if they have lost it they just need to pay me the money I'm owed. I've just checked Google reviews and they seem appauling - given these guys are recommended by Apple, does anyone know a way of escalating the problem with Apple?

[Re-Titled by Moderator]

Original Title: Apple Trade In