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)
Creative Labs
ASUS
Gigabyte
Dell
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.
Cisco
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:
AT&T (shockingly)
T-Mobile
Anker/SoundCore
Corsair
Microsoft
Sony
Phanteks
Fractal Design