After waiting for a replacement part for my Zortrax M200 Plus 3D printer for 4 months, I complained, politely but publicly, about bad customer service on the Zortrax 3D printers users Facebook group. I got contacted by a Zortrax customer service representative the next day, who took my printer serial number and looked into it. He confirmed that they had to manufacture the part that needed replacing, and said they would send it "soon". A week later the replacement part arrived at the shop, and I now have the printer repaired, up and running. Yay!

Now this might have been coincidence, or it might be that complaining publicly gets you on top of the pile of requests being handled. I can't be sure. But I'm happy it worked out that way.