I forgot how to look up the mobile phone number I used a few years ago.

I forgot to check the mobile phone number I used a few years ago as follows:

1. If in doubt, please contact the operator. Bring your ID card to the operator's business hall, provide relevant information, and inquire about the mobile phone number used in the past.

2. Find old phone bills and SMS records. If you still have past mobile phone bills or SMS records, these records may show the used mobile phone numbers.

3. use your mobile phone number to query the website. Look up websites through mobile phone numbers online and enter personal information, such as name and ID number. These websites may help you find the mobile phone numbers you used in the past.

4. Inquire through social media. Search your name or other related information on social media, and sometimes you can find the mobile phone number you used to use.

5. Go back to the phone book. If you have backed up your address book, you can retrieve the phone number you used in the past through the recovery function. Use cloud services provided by mobile phone manufacturers, such as Huawei Cloud or millet cloud, to restore the address book.

6. Check the old mobile phone. If you change your phone, the old phone may still have address book information. Try opening the old phone to check the address book, or use the SIM card slot to see if there are any stored contacts.

7. Ask for an email address. Many applications require a mobile phone number when registering, and they may send verification information to an email address. You can use keywords such as "verification code" and "mobile phone number" to search in the mailbox to see if there is any mention of the mobile phone number used in the past.