I upgraded my iPhone and when I signed in to the new iPhone from my Apple ID, it stored my iCloud data on the new phone, but the data was incomplete as on my old iPhone. I couldn't complete the backup due to full storage (I had extra iCloud storage but my phone kept telling me that there was "no space on the iPhone")
I needed all my WhatsApp chats back on the new iPhone, but couldn't get all of them and meanwhile I kept switching between WhatsApp apps on both my iPhones (haven't deleted it from the old phone). I tried backing up WhatsApp data on the old iPhone several times again and meanwhile was also backing it up on the new iPhone. Somewhere in between, on the new iPhone, the WhatsApp media files disappeared. Now I have access to neither my old WhatsApp chats nor any of the media on my new iPhone. What is the solution?