I’m trying to log in my iCloud account but it won’t let me because it’s trying to send me a verification number to my old number

You have to start an account recovery from:

https://iforgot.apple.com/

Enter your apple ID.

You will first be asked for the number associated with your account.(your old number)

You will need to enter this.

Then follow the steps.

You should be able to select that you dont have access to that phone number anymore and give a new one.

After that an account recovery will start.

More info about account recovery:

Recover your Apple ID when you can’t reset your password - Apple Support

See if anything here helps.  If necessary, you can use account recovery as explained above.

Verification code - how to get one and sign in with two-factor authentication.