Faulty car bought from WeBuyCars

So I bought a BMW a week ago from WeBuyCars with a DEKRA sticker on which to me means that the car is in great shape. Just to find out after having the car for not a day that it has so many problems. I made contact with them the same day when I encountered the issues and was told they would collect the car on Saturday then they didn't pitch so they told me they would collect on Monday and still didn't pitch. I however got a mechanic to service the car as per their instructions that the car only needs a service. The mechanic encountered so many other faults that has costed me a couple of thousands later and still the car has more problems. I contacted them again today and the manager had such a bad attitude whereby the problem was theirs and not mine. They got a new sales rep to sell me a faulty car. This is not acceptable and I want my money back ASAP and they need to fetch their s****s.