incorrect billing

I have been with Telkom for me the 3 years and my sim contract is due for an update . received an my monthly invoice 06/11/2021 with an invoice of R1348.04 which actually came surprise , knowing that my normal monthly invoice is R749.04 . Contacted the call centre agent to query on why my bill almost double and was informed that my spending limit was increased , i explain to the agent that i am not aware of this and that i would never increase my spending limit due to the bad experience i had when i took out my first contract with telkom and secondly the plan that i have covers my whole month , i have my initial contract that clearly stipulate that my spend limit must be kept R1. i have been in contacted with telkom ask them to assist me with resolving this matter and my debit order is due now on the 20th and i have not made an provision to pay that amount , so now i will have unpaid debit order and penalties for something that i didn't give any consent with . a case number ***7 was provided and has not been allocated to any to give feedback on what happened and as to why my spend limit was changed .