WhatsApp restore after swapping to e-SIM

[ERS22]

I have tried to transfer my WhatsApp to a new phone after switching my number from physical SIM to e-SIM. Before transferring phones I backed up my WhatsApp. That backup is definitely on my iCloud Drive, but WhatsApp doesn’t recognise it’s there. After a lot of investigating, I realise the WhatsApp on my old phone seems to be under a different number after switching off the physical SIM. I didn’t request this and my contacts haven’t been notified of a number change. 
My problem now is that I have a backup on the iCloud I can’t access because it’s not associated with my WhatsApp account. On Public Mobile I have transferred the associated number to the e-SIM and receive texts and calls just fine.

I tried to use the Whatsapp QR code feature to transfer chats instead but could never get the prompt to come up. 

Anyone else had this issue, or know how I might resolve this to restore my WhatsApp?

[will13am]

@ERS22 , this is the process for changing the phone number associated with a whatsapp account.  You need to that on the old phone unfortunately.

https://faq.whatsapp.com/498754122134583/?cms_platform=iphone&helpref=platform_switcher

[ERS22]

I have no idea why it would become associated with a new number. I assume it’s a dummy number given by Public Mobile once the physical SIM became inactive? 
I considered transferring my number back to the old phone to try re-do the backup but if the iCloud Drive backup is now associated with this dummy number it won’t help

[hTideGnow]

@ERS22 why would the WhatsApp on the old phone associated with another number?  You can try access WhatsApp using wifi on the old phone and try backup again.  Worst case, buy a eSIM in the old phone and backup WhatsApp and then buy another eSIM on the new phone after (Sorry, eSIM is very troublesome in switch8ng phones)