Well, I sent their contacts listed on their IP allocation a mail yesterday morning about the issue after I logged a ticket with SAIX, and after 2 business days they haven't responded. Vodaxom has been doing some investigation, and determined the problem is on the ETC side (they put one of our IPs on their router that peers with ETC, and from that source IP could not reach the sanral site).
Definitely a routing or access-list/firewall problem, but not necessarily bgp.
None of the comms from Vodacom showed any comms with ETC/SANRAL, but the SANRAL call centre said they had logged a call with the 'service desk'. So they seem to be aware of the problem.