Carry the car seat right to the actual plane where it will be put in the hold afterwards.
Don't forget to declare it at the check in counter, they will give you a tag for the baby seat.
For sizes, call the airline you have booked with.
Very painless process, don't stress about the admin here.
The airport may work, but the 31 million traffic lights leading up to it do not. That makes the drive to Lanseria a terrible experience, especially from the Johannesburg end.
Besides, flights are usually more expensive than OR Tambo.
Wouldn't a stopcock key work?
(Get your mind out of the gutter guys)
Something like this, first link that I found. May be cheaper elsewhere.
https://www.bobshop.co.za/4-way-faucet-key-sillcock-water-key-2-pack-multifunctional-utilities/p/634275208
Going to save you some trouble and explain.
This is a public Internet forum, not a Vodacom support service. You're going to get actual assistance from Vodacom directly. Call them repeatedly or go to a store until you get someone willing to help.
Ignore the pictures comment, people are being...