New engine

I bought a opel course on 27/07/15 from williams hunt I have had numerous of problems with this car but now after servicing my car on the 1/09/15 one month later I realise that oil and water is mixing and I sent it back to them and now the are telling me I need a new engine and I have to pay for it .the service has been so bad I have been with out a car for over a month now and no one had called me to give me any feedback only when I phone did they Decide to Give me some feed back and because. Reggie was on leave no one was there to attend to me.this is not customer service if u forget to give your client feedback. and I took a extended warranty on my car and yet I still have to pay for a new engine and I have only driven 6000 kilometers since I picked up the car till now