Hi lavinia228,
Your Apple ID is the account you use to access Apple services,
such as the App Store, Apple Music, iCloud, iMessage, FaceTime and more.
You might want to get all the current details up -to-date via your Apple ID account.
You can sign in to all Apple services with a single Apple ID and password.
Apple Support have articles online that may help:
Manage and use your Apple ID
https://support.apple.com/en-au/HT203993
If you forgot your Apple ID (usually an eMail address) and / orApple ID password
or
If you have issues when you try to sign in :
https://iforgot.apple.com/password/verify/appleid?r=1&language=US-EN
If you’ve forgotten the answers to your Apple ID security questions
https://support.apple.com/en-au/HT201485
There is another discussion thread with relevant info on changing the phone number
https://discussions.apple.com/thread/253338131
There is info. on accessing the old iCloud account in this discussion thread:
https://discussions.apple.com/thread/253302653
And:
If you make changes to your Apple ID or Apple ID password:
What to do after you change your Apple ID or password:
https://support.apple.com/en-au/HT204071
Other resources:
Apple ID Support website:
https://support.apple.com/en-au/apple-id
And
iCloud Support online:
https://support.apple.com/icloud
There is also a "Get Support" link to Apple at top right ion this discussion page.
Hope this helps you :-)