Tech-related companies with which I've had poor experiences with their customer service/tech support departments:
Kia (a specific dealership, after which I spoke to corporate who came down like the hand of God on them)
CyberPower (the power systems manufacturer, not the boutique computer builder)
HP (now HPE, specifically in regards to their Procurve PoE switches)
Anyone making a tech product via Kickstarter, consistently, every time.
90% of people I've purchased tech from via Ebay...though Ebay itself is great.
Tech-related companies with which I've had a good experience with their customer service/tech support departments: