Evri complaint: Lost valuable parcel being returned to sender.

My parcel arrived days late and damaged. The driver saw this and said do you want me to return it to the depot as damaged and return the parcel to sender. I agreed. He then took a picture of it. That was Saturday the 2nd of November. Tracking it it then said it had tried to be redelivered on the Tuesday. Which made no sense. I then heard nothing. Contacting evri by phone I just get the same message from when it was first delayed saying contact sender for refund or replacement. I started a chatbot to which I requested a telephone call. I got an email stating they’d look into it. Then one saying it was lost. The value of the item is £400 which the seller is telling me that they won’t refund me. As I should have not sent it back via the courier they chose but another and its my fault it’s lost. I tried multiple times to get in touch with Evri to no avail. I just keep going round in circles. This is the worst customer service I’ve ever come across. Am I just supposed accept a £400 loss and not be able to hold anyone accountable.