Horrible customer service - still waiting for paid-up letter

I have settled my standard bank credit card account in full as 16th May 2020. I requested for the account to be closed and to be emailed a paid up letter on the 26th May 2020. I have not received the paid up letter as to date. I have called their customer service, credit card division on mumerous occasions but still nothing. I requested assistance with the matter from their Facebook customer service team on the 2nd of June, still nothing. I sent a complaint to their complaints resolution centre, still nothing. Yesterday I called the complaints resolution centre to check on the progress of my complaints and the person spoke so soft and sounded disinterested in what I was enquiring about that I needed to ask him to repeat his messages numerous times as I could not hear due to a low volume / voice projection. As it is today I am still waiting for the paid-up letter, that I urgently need to use.