I want my money back

I sold my car to this dealership in January, they paid me 10k as deposit within 3 days ,on the 4th of March they called saying on the 5th they will make a payment and they ddnt, I understood because they promised to pay the following week which was the 11th of March , in the 11th of March they promised the 12 when I call their office I speak to about 4 people not knowing who will assist me or tell me the relevant person to assist is not in the office , they said they are waiting for a Cheque to reflect that was the 11 till this very day I haven’t get my payment,the director or owner Lisa the whole of last week she was promising to pay the money latest last week Friday today it’s Monday she’s not calling or letting me know what’s going on , it’ now my duty to call them every day and ask for my money ... they have the trashy customer service ever and if you are planning on selling your car to them DONT those people they don’t value their customers let alone to respect customers, they are inconveniencing me and messing up my life , because I make arrangements with other businesses with that money and find the day they don’t full full the promise ... I’ve been very patient and understanding I can’t take it anymore I want my money