Bill still wrong after 6 months

Good day to you.<br> It has now been more than 6 months and still Telkom is billing me for a service that cannot be provided. I initially signed up for a 10Mbps line with Telkom @ R899, but due to the distance that I am located from the exchange, only a 4Mps line can be provided. However, I am still being billed monthly for a 10Mbps line....surely this is not correct and my bill should be adjusted accordingly? This matter has been raised more than once and this matter has still not been addressed.