I had a similar issue with a Wyndham property that said they couldn't provide an itemized bill because it was booked and prepaid via Wyndham. At the time I thought the staff didn't know what they were doing.
Based on this OP report, I'd think that they do have a system issue were the central reservation system doesn't transfer the transaction detail to the property system... Given other Wyndham system issues I have encountered, this wouldn't be a surprise.