What are your line statistics? Specifically, noise margin and line attenuation. Also, if your router reports errors (e.g. CRC, LOF, LOS, etc.) post those as well.
IS = Internet Solutions. It's an Internet Access Provider (I think that's the correct term - think of it as an "ISP for ISPs"). It competes with SAIX, which is essentially Telkom. The line provider is almost always Telkom, although these days you can pay your ISP your DSL line rental.
It boils down to this: IS provides satellite-based international connectivity (e.g. the Uncapped Express Accounts) as well as fibre-based international connectivity (which is the IS Fibre Semi-shaped product I mentioned to you). SAIX provides fibre-based international connectivity (which can be shaped or unshaped).
Nexus is an ISP, just like WebOnline, your current ISP. However, they offer a monthly/capped account of the
IS Fibre Semi-shaped kind, which in my opinion, is far superior to SAIX shaped accounts (which is probably what WebOnline provides you with), although R11 (or thereabouts) more expensive per GB than SAIX.
If you want to try IS Fibre Semi-shaped to see if it solves your problems, you can purchase 1GB prepaid for R89 from
Axxess.