Thanks Raffele, and all of you.
The mysterious 4th. ticket was refunded so I don't have grounds for action there.
At present, the situation is that I've been charged for 6 tickets and refunded for 3, meaning that (and this is not higher mathematics although it seemed to cause one numbskull at SAA a problem, I said to her it's 6-3=3 but she seemed to have a problem with that) I've ended up paying for 3 - which is correct.
My losses on the transactions result from the consequence of the debits being converted from ZAR to GBP at one rate (plus the 2.75% credit card rate) and then when the refund for the same amount of ZAR was converted to GBP the 2.75% was again applied, plus any exchange rate fluctuation, meaning I got back less than I'd been charged.
When I discussed this by 'phone with my CC issuer in UK the person didn't seem to think they could do anything, so I left it at that on the basis that these things usually only get proper attention if put in writing.
It's now become a matter of principle rather than of the £60 or so that this now racks up to. Never mind my time.
SAA got a 4 star Flytrax rating based on their inflight service (which is generally very good) and probably does not cover administrative matters. Their after sales service is an utter disgrace and should also be rated. On a scale of 1-100 I'd give them -20.