They Use Juniper i think, I did email support about this about,
http://forum.mikrotik.com/t/mikrotik-l2tp-client-to-juniper-device/68795/11
Is the same request, I think this is also from south-africa looking at the thread,
If you need additional information then i can provide you with everything you need, supouts, remote access to an unit connected to the infrastructure that can allow you to test.
here is my ticket for this request Re: [Ticket#2013091666000226] Your static IP address has been allocated.