I'm so sorry.
Sorry to keep you waiting.
It's totally my fault.
Hopefully we can get this problem worked out quickly.
I'm sorry. I called the wrong number.
Sorry to bother you when you're busy.
Sorry, it wasn't on purpose.
I truly regret the troubles I caused.
Oh, I'm sorry about that.
I am really sorry that I am late.
I was in the wrong.
I'm sorry to make you wait.
I'm very sorry to have kept you waiting.
●●, I am sorry for what I said; I didn't mean it.
I was wrong. I owe you an apology.
I'm sorry I scared you.
I'm sorry I forgot to reply to your e-mail!
Sorry to surprise you.
I'm afraid I won't be able to make it.
I'm sorry for making a mistake.
I apologize from my heart.
We appreciate your bringing this issue to our attention.
Sorry for the delay in reply as I was out of office.
I'm sorry about the absence without notice.
I should have double-checked first.