Lights are on but nobody at home

I have been waiting over 2 weeks for an invoice to be amended. This has happened before even in non lock-down times. Fedex is always quick to take your money, but when there are queries and faults with clearance they are nowhere to be found. No one really cares or answers when they arent able to assist. All I am being told is that it has been passed on and they have asked someone to assist but clearly nobody is really actually doing something about the matter. I have lost orders and lost income so many times. My clients use FEDEX but i will myself never make that mistake.