Hold on Zoe ;-) This is a good shot, but it has a few errors.
"Raised by" is fine; you 'raise an invoice' But I see no need for the passive voice here - it just makes it harder to read (and to write!); the same goes for 'paid by you' (it's true that official documents often use the passive, to sound more detached - and so a bit threatening - but that's no reason to copy a bad habit). And I see no reason for the abstract noun phrase 'in reference to' - which just increases the Fog Index (
Text Content Analyser - UsingEnglish.com - the UE text analyser is a great resource. Give yourself a pat on the back, Red5. ;-))
Why not say 'We refer to our invoices XXX and XXX. You have underpaid by £2000.00. Please check and settle in full asap, and re
fer back to me if anything needs clarifying. ['I attach copies of the invoices' - though maybe this is unnecessary, except to make it clear, for the record. that you sent them copies] ?
b