why the verification code doesn’t work?

Not if you have 2 Factor Authentication or 2 Step Verification turned on. Have you tried to get a new code?

See if anything here helps. 

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

If you have to step verification on, and you've had it on for at least two weeks, you cannot turn it off. There is no other way to sign in (But if you still have the same phone number it can text you). Please reply to me if you need anymore help.