That's because unless you got the accidental protection plan it's not covered.
The standard warranty protects against manufacture defects and normal "wear and tear" on the device. A cracked LCD screen is not normal wear and tear. But the accidental protection plan would cover things like dropping your phone, spilling liquids on it, etc etc
This.I don't doubt what you are saying is true, but the salesman are either uninformed or straight lying. Eitehr way, its a scam. Don't bother buying it.
