Trade-in Value amount different?

 I got a long in writing estimate claiming I would get $400 credit for my iPhone 8 for a promotion to upgrade to the 13 I ordered it online and got the new phone was preparing to send the old one when I read the "updated offer" saying $75 are they stupid? They can't say it's based on condition of the phone if they lowered it without ever seeing mine it's flat out false advertising lies it's wrong in every way.. needless to say no thanks I'll either keep it just in case or I'll resell it on my own for at least 2-300 but sending it to them for 75 after they clearly offered $400 they have to be out of their minds! Law suit is over due