Telkom the bullies

I have had the most terrible experience with Telkom. I have been handed over as I closed the account they used to debit me off even though I have returned their device. Device was initially issued by mondlo and in the emails I have been corresponding with them in, they say the fault is with Telkom. It has been over 2 years now and no one is assisting me. No matter how desperate you are, never get a contract with Telkom, that was one of my worst mistakes I have made in my life. I honestly do not know how to sue them as they have tarnished my name and at the moment I cannot even get credit. If anyone sees this and can I assist with the procedure to sue kindly assist. I am honestly fed up with these bullies.