get a taxi
I had to leave early because I
wasn’t feeling well..Have to suggests that someone else or some outside authority
or circumstances makes it necessary.
Must is prefered when the speaker decides it is necessary and
to express urgency with you and in public notices.
I have to see the headmaster (..she has called me to her office)
I must see the headmaster (...I want to discuss something with her)
I have to work from 9:00 am till 5:00 pm.
I have to pay my road tax soon.
You must start working harder! (I say so)
You have to turn left here.(It is the law.)