I cannot perform WhatsApp backup

Good day, 

I have tried for days to backup my WhatsApp chats as I want to change to a new iPhone. 

My current phone is an iPhone 7. 

I have tried: 

1. Rebooting my phone (many times)

2. Hard reset of my phone (thrice)

3. Deleting my entire iCloud backup and then backing it up again

4. Disabling backup of WhatsApp to iCloud and re-enabling (many times too)

5. Deleting the past back ups of whatsapp from iCloud and my phone

6. deleting messages and media from WhatsApp 

I've also ensured my iOS is the latest version.

Now my WhatsApp app says last back up was “never” and every time I try ‘back up now’, I get the pop-up error message “Couldn’t complete backup. Tap “Back Up Now” to try again.” 

Can you please advise? I don’t really trust the third party apps for backup and they cost quite a fair bit. (unless someone here can recommend a good one reasonably priced?)

Thank you & regards 

Priscilla