Leave. I'm in the final week before my line and ADSL switch over to another ISP, and it's been a damn long 30-day notice period with Telkom, I tell ya.
The best part is Telkom doesn't even care. When I phoned to cancel, the rep asked me, 'Ok, so what's your reason for cancelling?' and I answered 'Constant buffering.' The rep just said, 'Aah, ok.' and that was that. Cheers mate.
Contrast that with Outsurance's amazing retentions department ... it's easier to murder your mother than leave Outsurance, and that's the truth. Best of all, they kill you with love, and increasingly better discounts and faster-talking retentions specialists