Sometimes the OTP gets stuck somewhere, this happened to me last week.
First check your email settings, make sure your emails are coming straight through, and it isn't blocking the ESO site. These are sometimes changed by the emial system (happened to me once or twice).
If that's ok, try logging in via the other route, ie if you previously tried logging in via the client, then try logging in via the ESO accounts page, and vice versa.
People believe what they either want to be true or what they are afraid is true! Wizard's first rule
Passion rules reason Wizard's third rule
Mind what people Do, not what they say, for actions betray a lie. Wizard's fifth rule
Willfully turning aside from the truth is treason to one's self Wizard's tenth rule