I once had a very annoying problem with a DHL parcel station (in Germany). at some point I was so fed up that I looked up the names of the C-level management, guessed their email addresses and sent all of them a message. didn't really help much in the end but I got a response and it was internally escalated apparently.

I did similar when I was planning to move. The new place was just a block away from my old address and my ISP told me my new address does not exist. After more than a month of arguing with their customer service people and being told there is nothing they can do, and with time running out for my move date, I got lucky. I somehow found the email address of a vice president at the company. After one thoughtfully crafted and well targeted email, 45 minutes later I had a supervisor and a technician at my house to do a site survey.