Cellc charging debit order fees for a R0.00 account balance

My husband cancelled his Cellc contract last year when it reached its 24 months and gave a months notice. On 8 Oct 2023 we recieved an account for R95.51 which we paid via eft on 9 Oct 2023 which means the account should have been zero and then closed, every month since then we have been receiving an account for a R70 failed debit order fee, as of April 2024 we owe R350 in debit order fees because Cellc basically tried to debit a zero balance. I have been emailing customer services since November 2023 with no help, all I receive back is an acknowledgment email.