Horrible and frustrating experience from Telkom

I app**** for a cellphone contract from Telkom. It was delivered and stopped working the next day. it was collected by the said company and I never received any feedback from them afterwards. I asked for the contact to be cancelled as the phone could not be replaced. Long story short: The amount that I owed was written off and on the 29th June 2017 the written-off amount (R583.71) was reversed. This is baffling because I have no idea what it is that I have to pay for! Now I cant access a home loan because this keeps appearing opn my credit profile/history as an overdue amount! Phoning their call-centre is futile because you get several reference numbers and nothing gets done about it!