TransferWise takes customer support extremely seriously with an in-house team of support reps who are trained in all of our features. On top of that each team may have one or more CS "champions" who are the bridge between product teams and customer support. These champions usually know the product inside-out, and are in slack channels with the dev teams.
So when an issue is not a customer misunderstanding something, and turns out to be an actual bug, the CS rep will work with the engineers to find a workaround, and to get a fix deployed as fast as possible - all while the customer knows exactly what's going on.
Bottomline is that I agree that customer support is hard, and very expensive. But it doesn't have to be broken, and I don't think it is at TransferWise (well, Wise now)