Common Mistakes in English
Don't have to = Do not have to We have to use don't have to to say that there is no obligation or necessity to do something.
For example: "You don't have to do the exercises at the end of this page."
Mustn't = must not is a modal verb used to show that something is not allowed. When you use mustn't you are telling people not to do things. It has the same force as don't , as in: Don't do that!
For example: " You mustn't drink if you're going to drive."