Telkom Mobile Overbilling issues... Pathetic service

I Signed up for an LTE Telkom Mobile contract about 1 year ago. I Have had about 6 months or regular billing and the rest is just overcharge after overcharge after overcharge. After eventually speaking to a person in Pta that understood what i was saying they sorted out my billing. Again the last two months they keep over billing me and leave my complaint open. line keeps dropping and they don't even phone you back. Again i am left being billed with no recourse. Are Telkom not in Breach of their contract by doing this? What can be done legally to stop this from happening? Any help will be appreciated..