Sanity check here please.

I have just arrived in J on Qatar QR131 on a DOH - FCO flight
I have an onward flight in a few hours on BA557 FCO LHR in Y. I only have Ruby status, si I can't get into the lounge based on status.

My understanding is that the BA FCO lounge should count as a one world lounge and I should be granted access based upon the same day international long haul OW flight, but the lounge attendant isn't having it.

Anything I can reasonably do, other than pay for access and try to send the bill to BA?