Vodacom contravening NCA, and claiming undue fees

I ended a month-to-month contract with vodacom in March. My April statement and invoice shows zero outstanding balance due, as would be expected with a post-paid contract via debit order.

Blow me down when I get a letter in September from Vodacom Collections, stating that I owe an amount (dissimilar to my previous monthly account fee).

I request some kind of supporting documentation, and am proceeded to be completely gaslit by Vodacom.

Baring in mind this was a credit agreement, which requires statements to be issued detailing any outstanding amounts. By claiming this amount they are in contravention of the NCA.