Once, long ago, I ended up buying the wrong ticket from Deutsche Bahn. I no longer remember whether this was my fault or theirs, but I do remember that support was completely unhelpful. My credit card provider was considerably more helpful when I solved the problem with a chargeback.
I know of instances where the end result of a more than half a year support escalation process of the highest instance said "you (the customer) did everything correctly, but our support provided wrong advice. Bad luck though, as we don't consider ourselves accountable for mistakes in the support process. Please stop contacting us."