Goodafternoon please assist me I have been harrassed by Mbd that I am owing them 36000 as an interest

Goodafternoon please assist me I have been harrassed by Mbd that I am owing them 36000 as an interest. I was owing Woolworths credit card 42000 when I was handed over to them 2016 paying 1*** I stopped paying because according to my calculations I am done paying. 2018 legal aid asked for statement because different consultant's will call me giving different amount that I am owing 75000 even now there saying Woolworths handed me over with 75000 last year may I am confused when I ask them what are they seeing on the system respond you have 2 account's I have only credit card that I was handed over they say one is closed other still owing that I don't have I think there changing me double interest. I am getting calls everyday explaining same story how can I owe 75000 from 42000 even though I was paying please assist. I know that's a **** of people buying books from companies to harrass us for payment. Please assist