A friend of mine

stayed at an international chain hotel recently.
On checking out he - or she - attempted to apply a monetary discount voucher to the bill. Front desk didn't really know what to do so made some phone calls. This whole scenario took around 20 minutes and at the end the receptionist simply cancelled all charges - including taxes - other than a small phone bill.
This significantly overvalued the vouchers and was brought to the attention of front desk, but they said that was that.
A few points have now posted to the guests frequent stay account. Can the hotel now audit the bill and try to claw back the correct rate via the credit card left as an imprint?