Vocabulary
I had an appointment.
I unfortunately have to cancel the appointment.
Unfortunately, I can't come. 
Unfortunately, I can't make it.
Ich bin krank.

I'm sick.

I have an important appointment.

I missed the bus. 

I'm coming a bit later.
I'm sorry.

Can we change our plans?

That's too bad.

It doesn't matter.

We'll arrange a new appointment.