Right, so after having logged a complaint with SANRAL ages ago regarding inability to actually pay for outstanding amounts, they finally got back to me yesterday with some dodgy information. I asked them to clear up some things and they have now phoned me with the complete info.
Apparently though, they won't provide any form of receipt if you pay via EFT. The only way to get a receipt is by going to a store to pay. According to Thumelo Phefo, the gentleman who phoned me, they are in the process of acquiring my details from ENATIS and once that has been achieved, they will send me an invoice. If I don't pay by the 14th of this month, I'll be paying the penalty fees of roughly 3.7 times the current outsanding amount.
Best case scenario, they get the ENATIS info today and send the invoice. It's pretty unlikely that I will receive it (thanks to wonderful SAPO) by the 14th of this month, meaning that by default, I would be liable for the increased amount. For the record, the increased amount is around R223 for a single Southwards trip down the N1, hitting all the gantries on that highway. Pretty expensive for what, 60km or so?