Printer on Warranty but I paid for Repair

I bought a Canon Printer at Game store through Account from Game. I took it for repair to Game Store Phalaborwa while not having Invoice but having a proof having bought it there since Ive used their account. The Printer was still under Warranty but Ive paid for repair of the printer. They managed to allocate a proof of me having purchase the printer from them. When they took it for repair they indicated that the invoice is not clear and I should Pay for repair. Ive Paid it and Please assist me in claiming the repair costs.