What does 'Original product return pending' mean?
iPhone 6, iOS 9.0.2
From your post
Apple has declined to repair your device for some reason and the repair center is preparing it for return to you. You can always call them and ask what is happening, but otherwise, I expect you'll get an email in the next few days with a return shipping notice and some explanation of why they declined to repair it (Possible reasons would include evidence of water damage, accidental damage, or something else that voided your warranty and support).
The new year holiday may be the simple cause for any delay in getting it returned to you.
What does 'Original product return pending' mean?