Help with Telkom

After 40 years with Telkom, I cancelled my landline and Internet, in 2017,retaining only my TI mailbox service (email address) In January 2020, my email stopped working, I contacted my Internet Provider and was told that Telkom had made changes and I would have to contact them. I contacted Telkom and was assured it was a minor fault and would be rectified immidiately. After numerous calls, with no result and no email, on 18 March I registered a Gmail address and cancelled my Telkom email address. In April I received an account from Telkom, for IT Mailbox Service, I then advised the the account was cancelled and sent copies of cancellation document. I have just received an account for May for IT Mailbox Service. My account at Telkom is in credit so they just keep deducting. Can anyone help or suggest what I can do to get rid of Telkom