Supporting Documents not returned even after 3 weeks

[sksk123]

This is my son's first British Passport. I have got his passport 3 weeks back. I am waiting for supporting documents. Since this is his first British passport, I had to send his current US passport as part of supporting documents. I haven't received his supporting documents. I have booked tickets to India this week and I need his US passport since OCI has US passport details. I am very anxious since I have booked tickets, PCR test etc for the travel for the entire family(Travel Date: 18/02). I have paid for extra £5 for supporting documents to be sent by tracking. So it has to come by TNT. I have been checking TNT tracking and there is no new consignment for supporting documents. I have contacted HMPO few times by phone/twitter and web chat. Finally they are saying that they have sent the documents to TNT long back and TNT is saying they never received the document.
Has anyone had this problem recently? Do you guys know the process of transferring the supporting documents to courier provider? What can i do to speed up the process?. I need to get the passport within 2 days otherwise, i need to postpone the trip which is going to cost me so much stress and money.