I was trying to stretch the metaphor to make it make sense. No distortion intended (or I think, actual).
The metaphor falls down because if I pay TNT to deliver a point to point package then it’s just TNT that’s responsible. But we’re talking about a network with lots of providers, a core interchange function and different companies providing the end points. In which case the post network (where Royal Mail almost always does the last mile) but others can provide collection and sorting is probably a better, although not perfect, metaphor.
I think I’m out. But my advice to @D3LL remains - it can’t harm to contact Monzo. So I’d do that (as well as asking the sender what happened). But in the meantime, I’ll leave the passionate folk to it.