Poor pensioner service and no CPA ethic

My father a pensioner decided to support Liquidation centre in Goodwood by purchasing a Inverter to use doing this bad loadshedding. This was just over 2 months ago. The machine then stopped working, obviously still in warranty when taking it back to the store to either be fixed or replaced. They refused to assist as my dad had lost the slip. I however did produce a bank statement reflecting the amount as he purchased it on his bank card. After many words the lady was willing to book it in. But stipulated that if there was no slip they are not obligated to assist. That the unit will take 14 work days to fix. We are now on 19 days when I called I was told so kindly because I did not provide a receipt we will just have to wait for the repair. Any company should have the means and software on the POS systems to do reprints. Let alone refuse to even look for the pop for a 71 year old gentleman.