How complicated is it to close a paid off credit card?!?!?

I’ve been trying to cancel a discovery credit card for weeks now and they keep playing games. I paid off the credit card on the 20th June, sent confirmation that I had settled the card and even followed up with a phone call to ensure cancellation. I’ve been given the run around. I was told someone would call me to facilitate the cancellation, nothing! I called again and was sent a form to fill in. I sent it as required, no response. And I can see on the app that this card is still active. I am not sure what games discovery is playing but I’m very appalled by these tricks! How complicated is it to close a paid off credit card?? The aim is probably to start charging their exhorbitant fees and erode the paid up balance. Please close this credit card already and sent me confirmation. I’m tired of running after you.