Still paying after 30 day notice period

Surely this isn't right? I cancelled my month to month adsl line on 25th Feb 2019, I did this in store at Telkom Overport city. I then paid what I thought would be my last bill mid March to comply with the 30 day notice period. I then however got a message stating that my cancellation was only processed on 25th March 2019, and I am still receiving invoices two months later.

What is going on???