There is a very big difference between must not and don’t have to. “Must not” is like DO NOT! But “don’t have to” often means you can if you want, but it’s not necessary. Here are some examples:
You must not touch the hot stove.
You must not wake me up in the morning! I will be very cranky!
You must not drink milk that has expired.
You don’t have to wear a raincoat today, it’s not supposed to rain.
You don’t have to eat all your broccoli, it doesn’t taste very good.
You don’t have to go to school today because it’s a holiday.
Do you see the difference? “Must not” is more like a command, but “don’t have to” lets the listeners decide or conclude they do not need to do something.
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