Line cancelled in june 2019 but is still active and being billed.

Cancelled my line with them in June 2019 then noticed the account was still active in July 2019 and called and was advised by the agent not to worry the balance will be rectified as it was cancelled in June 2019. I noticed i was still being billed in December 2019 and was negatively affecting my credit record, called them to rectify this and provided them with the cancellation number and was given a case number, they deducted the amount owing and promised to cancel the line. In April 2020 i noticed i am still being billed and the account is note cancelled, it has been Almost a year and i have followed Telkom's instructions and yet it still is not cancelled, this is affecting my credit score. I before Telkom my credit record was perfect, after Telkom my credit score is average, it was the worst decision of my life getting a Telkom line. I recommend staying away from Telkom.