Thank you for sharing Katharina. ❤️ Working in a company that does B2B and a special kind of B2C (i.e. the kind where you cannot just "quit using the app and install a new one") this sounds very familiar. With users "bound to their products" the ROI of UX design is harder to measure. Sure there are the # of calls to support, but these of course only measure the kind of the problems that get users stuck. All their smaller and bigger daily annoyances, or the clumsy workarounds they have gotten used to go unnoticed that way.
We do get some feedback from our sales representatives that stay in touch with our customers, but that comes with a whole other set of challenges (filter in self-reporting, representativeness of feedback etc).
Nevertheless I love working in this area, it's really the complexity that makes if interesting I would say. :)