Original Poster wrote:
CEB-HKG-AMS-HKG-AMS
But, I assume,
CEB-xHKG-oAMS-xHKG-CEB
If you chage this to
CEB-xHKG-oAMS-oHKG-CEB
ticket reissue and tax recalculation at HKG is need.
Did 2nd agent waive(or collect) your HKG TAX ?
(BTW, CEB-oHKG-oAMS-oHKG-CEB is not permited as an Asiamiles award, so I assume outgoing is a transit)
Sometimes, TAX is collected at airport.
In my experience, additional charge at LHR caused by Y->C upgrade award was collected at the time of checkin.