Proof of purchase

Recently crashed my phone, so need to take it in for repairs but at the repair center they want me to bring along a proof of purchase which I misplaced mine. Called telkom I was told that I should go where I bought the phone went there I was told that they don't have my proof of purchase and I'm not on the system (but funny enough is that they still debt they money every month) how can one get proof of purchase at telkom? If I can't so will it be in my legal rights to cancel the debt order cause they don't have that I purchase phone. And honestly speaking telkom is just a sh@$;ty company has no respect for their clients.