Not happy with the service

I bought my car at Bidvest McCarthy in Woodmead and I was assisted by Tracia They promised to give me Cash back after 7days of me collecting the car also when I got my car it was low on fuel no full tank and she said when their drivers bring my registration number they will take my car and fill it up and they never did that .. she told me it will be included in my cash back it’s been a month now of waiting and they are not communicating I’m the one that had to follow up with them .. I am not happy with how she is handling this matter Can I get help so that I can get what they promised they will do a month ago… I am not happy at all