Bad Service

Hi, I have purchased an Opel Corsa 2009 Model from Emond Auto on 14/10/2014 It hasnt even been full 4months & I have had endless problems with the car, 1stly I had a problem with the Engine Management light coming on, I kept taking the car to them, They kept on reparing the 02 Sensor, No1 could explain why this has been happening, The 02sensor has been replaced 3 times!! I was accused of not driving the car properly! & Trying to pass the buck! In the past 2weeks the car has been using to much of fuel, Clearly there is something wrong! They cannot find the fault & said they have done a consumption test & everything is clear on their side. I now need to take it to CMH to do a diagnostic test to see whats wrong! I have emailed the managers & owners today asking them for the results for the fuel consumption test & the tests that has been done before I purchased the car, I was told that the previous owner traded the car in because of the management light beeing on & no tests where done! When I purchased the car I was assured that the car was in perfect working order! The Service I have received is shocking! They have their money + I have taken out an extended wareentee!