Billed on prepaid number 60 days after cancelation

I had a contract that was ending 25/05/24 and didn't upgrade,26/03/24 i called in for cancelation and was advised to call again on the 26/04/24 as it was too early and they work on a 30-day cancelation policy. Come 26/04/24 i called again for cancelation & they kept cutting my call, eventually after 3 attempts I managed to finish the cancelation process over the phone. 27/06/24 I received my invoice with the now prepaid phoned being billed for June, I called CallCenter and gave invoice number and consultant said she doesn't see that invoice, the 1 she has isn't showing that phone. I called again two weeks after to follow up and consultant says no it won't be debited. Month end it was debited, its now July and I'm being told that the contract was canceled on the 26th of May,30 days after I called that's why I was charged for June.