If you don't remember your trusted phone number and you've since changed your number, here are some things I recommend:
- Check your social media accounts, bank accounts, cell phone bill, email, etc. to see if any of those places have record of your old phone number.
- Ask friends and family if they have your old number saved in their contacts or old text threads.
- Obtain your 3 major bureau credit reports (Equifax, Experian, and TransUnion). There are official ways of obtaining these reports for free once a year. They often contain record of your previous phone numbers.
- If all of the above fail, try to obtain the original proof of ownership (i.e. the original sales receipt - not from eBay or another reseller) and submit it to Apple. They'll review your account and submitted documentation to determine if it's eligible to be removed from your device. You won't be able to recover your Apple ID without knowing the trusted phone number, but (if approved) you'll be able to regain access to your device to start fresh with a new Apple ID.
- If step 4 is not an option, keep hunting for that phone number. You don't need access to the number, you just need to remember what it is. This is to protect your information.
If you can't remember the number after all of the above and your device is stuck in Activation Lock, that's where it will be until you remember the number, unfortunately.
