No. The deductible charge was a line item "Accident Repairs - Renter Liability Deductible" on the final itemised invoice that included all the other rental charges, not a separate charge.

So the total credit card charge was for 1397.64, the deductible was itemised as 434.78 on the invoice (there was 15% VAT charged which brings the deductible up to 500.00 - but as a single separate line item for the entire invoice value), and the value of repairs performed was 777.24 (of which 500.00 was charged as the deductible). I specified this multiple times when submitting the documents, but they repeatedly (4 separate times) kicked the paperwork back asking for a Monthly Billing Statement showing the charge of 777.24 which simply didn't exist. Eventually, the 4th attempt of submitting the same documents with the same covering note seemed to have gotten through and they paid out.

Absolutely. I had a similar issue in Mauritius a few years ago and the adjuster back then approved the claim within a week based on the initial set of documents from Sixt.