Billing and imcompetent staff

I app**** for a contract which was granted on the 03/01/2018. I was advised that I was not going to be debited on the 25/01/2018, however it would debit with pro-rata end of Feb 2018. To my surprise I was not debited then and even in Mar. When I enquired and chatted with Thulani through Telkom LiveChat on 09/04/2018 I discovered that they captured an incorrect account number even after providing them with the correct details as well as my bank statement when I app****. I called the office in Rosebank and they also confirmed the incorrect account number that they had. I requested to speak to Nandi Maringa who was not available at that time and was promised a call back from her. She did call later on the 07/05/2018 and claimed to have the correct banking details. When I asked why was I not debited as per our arrangement, she failed to explain why. She escalated the matter to the credit department whom have failed to provide valid reasons as to why I was not debited as arranged. I requested her to provide me with a letter stating that the fault was not on my side for me to submit to my bank as I am applying for vehicle finance. To this day I have not received the letter however I was shocked last night when trying to purchase grocery that my card was declining. Upon me checking my account, I discovered that Telkom raise a debit of R2500 from my account which was not authorised. I did not have sufficient funds for that debit to go off my account which I know that it will cause my account to have unpaid debit orders and I will be charged. My credit status is being tarnished by the incompetency caused by Telkom staff. I do have screenshots of my chat with Thulani and the thread of emails from Nandi.