Silent_Bob is correct, the physical limitations of ADSL means that the maximum range is 5.5km.
However, although you are 8.5km in physical distance, perhaps the cabling length is shorter. When I applied for ADSL, I was about 4km from the exchange in physical distance, but the cabling distance was found to be about 8.4km. Telkom managed to find an alternate cable route that shortened it to 4.4km - which made ADSL possible.
Only way to find out is to call Telkom and get them to send a technician out to measure the cable length via impedance testing. If you are indeed over 5.5km in cable length, then there's not much you can do.