In this case it's not the GC who will do the paying anyway, so what does he care? The GC has an obligation to present your extra charge to the HO - but it is obvious he would rather argue with you than face a nit-wit of a HO who leaves messages on a holiday and expects everyone to accomodate.
Seems to me like the GC wasted some time here as well. And that's OK with him?
radar