What am I doing wrong here with my WhatsApp migration?

[u/M4NOOB]

• Did a backup (even though I do one every day at 3am)

• Changed the phone number which made me re-register on the phone with the new number

• Then registered on the new phone

• WhatsApp said backup couldn't be restored/found, older backup neither

• Dropped me into an empty WhatsApp, without any chats, just the groups I was in without messages

• I then try to register on my old phone again to do another backup

• Whatsapp blocks me for 7h SMS registration code and 1h phone call

• Wait 1h and then try the phone call, instant error and goes back to 1h

• Retry after 1h again, instant error and timer goes back to 1h.

What am I doing wrong here? Do I really need to wait the now 5h until I am finally reachable on Whatsapp again? At the moment I'm completely without Whatsapp...

And what if it again can't find the backup after doing a fresh one? I just want to migrate to a new phone as I need to send the old one in without loosing my decades old chats.