"The perpetrators of this variety of official language often fail to consider adequately who they are writing for,"
I agree, but the you follow with:
"can often come across as unsympathetic or overly officious".
Officious? Yes, the unwashed masses will understand that word, won't they? Even I'm vaguely guessing this is means something that sounds official and impersonal, without bothering to check the definition.
"We conclude that bad official language which results in tangible harm – such as preventing someone from receiving the benefits or services to which they are entitled – should be regarded as 'maladministration'," says the report.
Tangible, maladministration... does this person know who his audience is? Perhaps he does if he's talking to businesses, but for someone who states that he wants things to be clearer should practise what he preaches.
On topic, I think it's fair for a case to be closed until further information is received, or if the customer requests the same information again. No point in keeping it open forever.
Email/letter templates are there for the legal reasons (don't distribute, full and final settlement) and to prevent personal sounding pronouns, and generally you need to appear professional.
How would it be for a government of bank to write to you and say, "Sorry mate, but we closed ur accnt becuase you took to much moeny out and over your overdft limit. Signed, John.", would you trust an email like this, or one with a long signature with small print, and professional wording?
Jargon is something we live with and accept, even these legalese letters. It only matters when it is entirely related to your issue (i.e. relentless techie jargon on how to install windows, configure graphics) and you don't understand what is being said. That is when you need to tone it down.