Faulty Car

We bought a bmw 320 last year from McCarthy Toyota in Arcadia Pretoria through a salesman named Graeme after we bought the car we didn't get spare key,then they told us the previous owner didn't bring it with when selling the car to them,two months later the car started giving us problems with its electrical system but we thought it will go away as our wish to own a bmw was realized not knowing it was the beginning of our problems,the problem persisted till a few days ago when we took it to an electrician who discovered that the wiring system has been tampered with and had been bypassed so as a couple we feel we were given a raw deal by McCarthy Toyota cause we are paying for a car that is not sheering driving pleasure as it is suppose to be instead it's a headache,we want the entity to acknowledge its mistake and take its car back or refund us what we have spent on to fix it