I’ve had same issue at QT Canberra. I just use the credit for breakfasts and leave the discount for dinner. But yes it depends very much who you talk with - but I always ask to see the print out first as they try the ‘we will just email you the receipt trick’! I do enjoy a good robust discussion if need be however. It is no error on their behalf. Part of the course at this hotel…
I would be very certain it is the same staff member I had the issue with. I tried for a few minutes then left it thinking head office would sort it out. If I remember correctly their response was you will be able to use it next time you stay their. I also received a survey from the manager about the stay at the time and just left it knowing I was best to spend my time looking for another hotel to stay and avoid any future issues with that hotel.