Mobile contract is not proof of purchase

I did an iPhone 5s contract with Telkom. The phone is having issues. Telkom changed systems and has no record of the handset. Therefore will not honour the warranty through the master contract. They demand a proof of purchase document that was lost and did not inform at the time that this document is the phone warranty. All the information is online in their system though. They are unable to retrieve a copy of the document due to a new system.