Paying for a 10 mb line only getting 5mb down speed

I have been a Telkom client since 1991, service was not bad until 2010 once i switched over to uncapped. Once i got uncapped my problems just never stopped either no connection and being offline for 2-4 weeks before a technician came to assist. My newest issue is that since my upgrade to a 10MB uncapped line 2 years ago, I think there was only like 60 days of the proper service i'm paying for most of the time the highest down speed i receive is 5.5 - 6 MB of down speed. Then once I phone to complain the (***********) Helpdesk agent has the audacity to tell me that a 5.5 down speed is fine on a 10 MB line witch I'm paying upwards of R1000 where the service only justifies R699 MB speeds. This is very unacceptable and if any other service provider was available in my area i would gladly move without second thoughts.