Incompetence of doing a basic cancellation and then charge for additional month

On 12/05/2020 I gave notice at the branch in Vaal Mall as the data contract end date was 04/06/2020. it was stated that June 2020 will be my notice period as the last debit order will go off on 04/07/2020. On 31/05/2020 the number was disconnected and it was not active anymore. On 04/06/2020 I received an invoice on email stating that on 06/07/2020 I must pay the amount of R279.68. How does this make sense as the number was disconnected on 31/05/2020 already? So on 05/06/2020 I went back to the branch in Vaal Mall and Rebecca assisted me again. She has logged a call with the billing department to call me as apparently the problem lies with them. Today is 12/06/2020 and no one has contacted me yet. How *********** can a company be that we as the public are forced to use Hello Peter just to get a response or get things done. This is now the second time in 4 years that I have to use Hello Peter to ensure you *********** people just do what you are paid to do. Just note that I will not pay the invoice of July 2020 so do your jobs and ensure that this debit does not go off. I am so sick and tired fighting with companies who are *********** giving service to their clients. I want it in writing that you guys will sort out your ****. I will never make use of Telkom again and will not refer you.