Writing a good apology letter is always important. We can use it to ask for pardon in cases that we believe necessary (as misunderstandings, etc...). We must clarify the motive for which we apologize and try to propose some solution.
Dear ....... :
We are truly sorry about any inconvenience that our company could have caused you regarding to the obtaining of the document that you requested two weeks ago.
We simply want to send this brief note to apologize. We are conscious that we have caused an inconvenience and we have decided to reimburse all the money that you have paid for our services, as a sample of our comprehension in this matter.
Please, accept our more sincere apologie.
Staying to your entire disposition, we say goodbye.
A cordial greeting,