The few times we've had to complain we've started at the front desk and escalated from there (only once has the local hotel staff been indifferent). If after 24 hours the local hotel hasn't responded or resolved the issue, we call the Diamond line.

We've had really good success with the Diamond line and they always seem appreciative to hear that we've attempted to resolve the issue locally and given the hotel 24 hours to respond. At that point, they step-in (manage) and assign a case number to your complaint.