02,January XXXX
[Name of Recipient]
[Name of the Organization]
[Postal Address]
[City, State Zip Code]
Dear[Name of Recipient]
I sincerely apologize for missing your call.I missed your call at that moment because[the reason for not picking the call].I am sorry for that, and I promise it won’t happen again.
Please, accept my apologies.
Yours
[Your Name]