Waste of money and terrible support

I requested in March 2018 to downgrade my line from 10MB to 8MB as Telkom couldn't supply anything faster that 8MB to my area. I have the emails stating that the downgrade was successful. It is now July 2018 and they still didn't do the downgrade and they are still charging me for the full 10MB. Their excuse is that there was a bug in their system which didn't push the downgrade through but they also refuse to correct my account for their mistake. They also mentioned that they will keep billing me for the 10MB until they can eventually do the downgrade even though the mistake is on their side. This is not acceptable.