まことに申し訳ありません
I really don't know how to apologize to you.
I must apologize.
申し訳ないこと
うるさくてごめん
I am extremely obliged to you―overwhelmed with your goodness.
I am sorry it's confusing.
I am terribly sorry but,
Pardon me for interrupting you.
I'm so sorry I frightened you.
I am sorry to make such a claim on your friendship―presume so far on your friendship.
I am terribly sorry that I could not be helpful.