Cancelled line 30 days in advance but received invoice

Good day,

I have cancelled my line and adsl internet via the my telkom application on the 31st of April to disconnect my services the end of May 2018. After a while I received a call to confirm cancellation. I have just received a Telkom invoice which is incorrect as I am not using any of the servies and the adsl internet has been cut from the 31st of May 2018. I will not pay for this invoice, please sort this out ASAP and get back to me.