How do I disable 2 factor authentication

See the "Can I turn off two-factor authentication after I’ve turned it on?" section in:

Two-factor authentication for Apple ID - Apple Support

If it has been more than 2 weeks you can't. If it is less than that find the link in the email you received when it was activated and use it to cancel it.

Check your junk mail, it isn't an email for updating your device, when you turn on 2-factor authorization (and you have to do this unless your employer mandates and controls it) you do receive a confirmation email.