Check that all the words you have used mean what you intend them to mean. Think carefully whether they will be understood by the reader, and whether they are suitable for the type of letter you are writing (not too informal and ‘slangy’, nor on the other hand too formal and pretentious). Avoid, if you can, jargon, clichés and repetition.
Writers of business letters, in particular, often fall into the trap of using formulaic or highfalutin expressions so as to create what they imagine is a suitably detached and business-like tone. However, many of these expressions are nowadays regarded as relics of a bygone age or just plain pompous. It is always better to err on the side of simplicity and clarity – don’t use twenty long words where three or four short ones will do.
Try to get your message across using plain English: most everyday words are as appropriate in formal contexts as in informal ones. More often than not, the more familiar word will do the job just as well.
In this letter, all the writer is trying to do is explain why he delayed paying his account but, because of the style, it is too long and is difficult to understand.