Vodacom demanding pay for services never rendered - harassment and deformation of character

About 2.5 years ago I gave my 30 days notice and had my account closed from Vodacom and ported my number away from them due to pathetic service. Vodacom then *******ly billed me for services not rendered to an amount of R5500. They handed this account to lawyers who sent me the itemized billing. I responded by explaining each and every entry and provided them explanations to why I will not pay for services I never rendered. Instead of following up with me, they handed the account to other lawyers who insist that the only way is to pay the now R6500. Every month they report to the credit bureau saying I owe them money when I don't. I get called each day and receive SMSes every day demanding pay with threats of legal action while I do not owe Vodacom a cent. This is deformation of character and harrassment and I am going to get Vodacom sued for it.