Poor collection in Accounts department

I would like to raise my concern regarding the continuous calls and letters I have been receiving from your accounts department. I have been contacted daily after allegedly missing one payment, however the payment was not actually missed.

In November, my account was debited twice. I informed the consultant at the time and was advised that the extra amount would be carried over to December as a refund/credit. Despite this arrangement, my account was still debited again in December. In January, I intentionally ensured there were no funds in the account to avoid another incorrect debit while the matter was being resolved.

Since then, I have been receiving numerous calls and threatening letters regarding an amount your department believes I owe. I have already spoken to a team leader who confirmed that a credit note has been issued but has not yet been processed.

My concern is: if the payment is still under investigation or processing, why has my account not been placed on hold or suspended to prevent unnecessary calls and stress? The current situation is unfair, especially when the issue is still being resolved on your side.