Telkom keeps on billing though account has been closed

I've cancelled my account with Telkom on July 15th - that's after I didn't have Internet for over a month with almost no communication from Telkom. I switched to fibre with a different ISP. Telkom gave me credit for that month & emailed me the credit statement. A few days ago I sudden;y received a new account, with the credit gone and billed double - even though I cancelled the service. I contacted Telkom via Twitter DM, they asked for prove of cancellation which I provided. Since I showed the prove Telkom has gone completely silent & refuses to reply.