Irritating collections from VVM Debt Collectors

I had a contract with Vodacom which was cancelled. All documents sent and payment done. I have been getting phone call and SMS's from VVM Debt collectors. on the 16 July 2024, I received a call from Mohali from Vodacom. Mohali checked my account and noticed that Vodacom have mistakenly billed me for June 2024. My account was cancelled on the 30 May 2024. It looks like Vodacom did not advice Accounts Department of my cancellation. Mohali promised to contact Accounts Department to request a Credit transfer. He gave me a ref number:- ***. This morning I received a message from VVM Debt Collectors that I still owe R130-06. I request that they advice VVM and update that I have fully paid what was due to Vodacom. I am tired of attending to this query, it has been going on for too long. It's really frustrating and it will give me a negative credit listing. I request that this be attended to and closed. It's really irritating.