Please! Please! Please! help Me anyone at Telkom

Can someone please help me, I canceled my telecom account more than a year ago because they where trying to charge me R5000 a month for my home internet line and i was paying for 40mbs line and getting 20mbs now they are trying to charge me R5000 for Services rendered when i ask what i get threatened to be black listed how is this company aloud to just do what they want ? Telecom is literally harassing me for months now, I honestly wish i had never Used this Service if you can call it that.