Three other options:
There is as a tour company called Eco Tur.
https://www.eco-tur.com/en/home/
They may offer you a pick up. Not sure if they still do. They have done in past. Their tours seem to be well regarded too.
Otherwise you could try BestFly.
https://www.bestfly.aero/
BestFly is an FBO and will have a transportation option for crews and VIPs visiting on private jets.
Astra Aviation is a flight support company.
https://astra-aviation.com/angola/
It provides passenger and crew transport.
All options will be pricey but hopefully cheaper than IC and nicer vehicles than the taxi mafia. BestFly and Astra will probably be able to meet and greet you at baggage reclaim.