Still waiting for a cancellation letter, meanwhile being harassed by collections call center

I wonder if there is a black hole that all CellC queries end up in because this is actually unbelievable. I am still waiting for a letter confirming that a ********** CellC account is cancelled after reporting it in December 2021 already. Social Media manager Danielle Abrahams called me on Monday with a promise to get this letter emailed to me and I have still to receive this letter, MEANWHILE THEIR COLLECTIONS CALL CENTER CALLS ME 2 TIMES EVERYDAY FOR THIS SAME ACCOUNT. Please get this letter sent to me and advise your collections lawyers to remove my name from their list because I can’t be explaining the same thing to them everyday.