If you are late or can’t / don’t want to go somewhere, here are some excuses that you can use :

– My phone ran out of battery so I couldn’t call you.
– I was stuck in traffic for ages (= I couldn’t escape the traffic for a long time)
– My car broke down.
– Sorry, I won’t be able to make it, I have a doctor’s appointment.

Other useful sentences :

– Do you forgive me ? (= do you accept my apology ?)
– I’ll make it up to you. (= to do something good in order to be forgiven)