I contacted their chat support to tell them about it. The person on the other end was insisting that I might be using another Skype account where my other contacts are. Which of course I ain't since I'm not that stupid. He then suggested the stupid bullshit Tier 1 support usually does, like reinstalling Skype. I did as asked.
Then he asked me for remote control of my PC which I refused, because I have sensitive data on my laptop and I'm on a MacOS anyway. I then asked for my issue to be upgraded to a higher-level tier, because losing my contacts is unacceptable. Then he made an accusation that I haven't reinstalled Skype as asked and that I'm probably using two accounts, at which point I gave up.
Anyway, Skype sucks, it's been a week since I've lost most of my contacts which I've been collecting for about 7 years or so and their support is useless.
If you're relying on Skype for your business, stop doing that ;-)