Telkom is unable to cancel line

I have cancel my acount at the end of February 2019 but still pay for service not use. On 29 March 2019 Telkom send email that: "Dear Valued Customer, Your case no ********** 9 is resolved. Regards, Telkom | Business Connexion"

Still Telkom invoice me for this cancelled line. If I contact them they cancel it again but I still have to pay for service not use from beginning of March! Telkom even says it is my fault, as a client, that the line was not canceled as they had informed me on March 29.