Bad Service and deducting after cancellation

I have been to HiFi Corporation Centurion a month ago, i want buy a refrigerator, in the beginning everything went well and the service was great. 3 days later they phoned me to collect the refrigerator and to sign the documents, i have waited more than a half an hour for them to assist me, then i cancelled the deal, after 20 phone calls during the month for the cancelling and bad service i have experience the went and deduct the monthly installment for the refrigerator that i don't even have.