Closed credit card still being billed

I together with a consultant closed my standard bank credit card account on the 29May 2018. We found out the settlement amount and paid it up full. I cut up the card and threw it away. Now I still end up with a statement being emailed to me at end of June. I phoned yet again and they said I had to follow up and phone them again. What makes yourll so important that I must follow up. Why did yourll not follow up. Please wake up. Close the darn account. I think a significant percent of monies of all large concerns is theft. Its blatant theft.