10mbps line synchs between 800kbps and 6300mbps

For 2 years my adsl was (almost) flawless. From November my synch speeds marched gradually downwards from 10mbps to 2mbps over a 2 week period. Since then I've logged in excess of 14 faults online and with the call centre. Each time the call was closed with nothing being done. The result is that I now synch at somewhere between 4 and 6mbps but every second day local latency exceeds 2400ms (Fourways to Rosebank) and my download speeds are between 0.04mbps and 4mbps (no that's not a typo, my old \mweb big black box"was 15 x faster thatn Telkom's fastest dsl package when it goes pear-shaped). Once I even got to speak to somebody from the adsl support team who promised they'd sort it out"