Cancelled mtn contract

I was offered a contract online for MTn by the Mondo Consultant I agreed then later on my calculation I notice this is too much they dsv courier call to arrange for delivery I accepted the deliver after that I call their call center on *** and spoke to Melinda to cancel the contract she advice that I must destroy the simcards immediately as she did cancel it with reference number RC*** that was April the 21st or 20th now in November I start getting calls from Mondo Collectors stating that I owe them I won't pay a cent as I don't have account with Mtn and this nonsense is affecting my credit score card badly can someone sort this our urgently my cellphone number is ***