Missing iCloud Backup

Long story short...

1. I lost my iPhoneX
2. In the interim, I borrowed my mums old iPhone 6. Signed her out through Settings, and signed myself in using my Apple ID (Note: I did not do a reset on the phone).
3. I then purchased a new iPhone 13 Pro and tried to restore from iCloud backup. I was expecting to be given the option to restore from my iPhone X as I am sure I had iCloud backup enabled on it. However, it seems the only backups I have are a backup from my mums iPhone 6 and a backup from my iPad Mini.

So question is:

1. Is there any way for Apple or myself to check if I have any iPhoneX backups?
2. Assuming I did indeed have iCloud backup enabled on my iPhoneX:

a. Did signing into my mum's iPhone 6, and it creating a new backup, overwrite my iPhoneX backup?

b. Is there any way for me to retrieve and restore my iPhoneX backup on my new iPhone 13 Pro?

Thanks