Not sure royal mail lost my self assessment paper forms

Hello, I sent out my self assessment paper forms on Oct 20, 2023 with a tracking reference number by Royal Mail. However, the present tracking does not show the mail has been received by HMRC. Would you please advise what should I do since the deadline for paper forms was passed. I have to submit SA109 in paper form for split year treatment. Thank you for your reply.

Hi HKger2102,
We would need to access your record to check if your paper tax return has been received.
If delivered you should now have the tracking reference from Royal Mail.
If you  please contact HMRC we can review this for you.
Self Assessment: general enquiries
Thank you. 

Thanks a lot for your reply.