Please help Telkom is a froud

I took a contract phone with Telkom but I took it via mondo their 3rd party via the phone i was supposed to be paying R159 a month their first debit order was R679 I've asked them to close the account till today it's not done they say I owe them R2789 when i ask them for my sales call they refuse but they tell me the call it's my favour I've been after them for over a year now what do i do please help.