Just a data point for those interested.

I used the OW online tool to price my itinerary:

CPT-LHR-LAX-ANC-PHX-SEA-JFK-NRT-BKK-HKG-MEL-AKL-SYD-OOL-MEL-DOH-JNB

I entered my details and I got the PNR. No credit card was asked online.

I called BA South Africa (number is posted on BA website) and within 2 minutes they took my credit card (HK issued), they charged it in ZAR and I got the eTickets by email while still on the phone with the agent.