Unfair billing

In May I ordered a washing machine 15kg. Then I canceled my order the following day after realizing that at Game the machine was cheaper. On the 28th June when they debited my account the washing machine was also included and they debit R1190 instead of R570. I then called them and I was told to make an affidavit explaining everything I am saying over the phone. It's their fault not mine why should I be the one running around making affidavits and emailing them. My request was just a refund. My concern is that they did not deduct end of May why now?