MRP Mobile bad service

I received a letter from MRP Mobile on the 12th of march 2020 informing me that I am 3 months in arrears with my account and that they will put it against my credit record with the Bureau, instead I have instructed my Bank to do a stop payment on their debit orders since I terminated my contract in a written email to them in October 2018, I only realized three months ago that they are still debiting my account with R90.00 pm. and yes they did just that, recorded me as a bad payer with three months in arrears which I confirmed with Clear Score today, this after I explained myself on a voice recorded phone call to a lady from MRP mobile by the name of Pretty on the 13th of March 2020, I did request a ref. number which I got but do not have it on hand now. Pretty confirmed that they did receive the termination letter and I made her aware that MRP Mobile owes me money as they never stopped presenting the debit order after termination, Pretty confirmed that she will address the issue immediately with her support team, she will give me a call as well as sending me an email once sorted, today is the 18th of March 2020, have not received any communication but instead they ruined my clean credit record, I will not back down from taking legal action if this matter is not resolved within the next 12 hours. I am disgusted in their way of dealing with their customers.