Pay back the

My car was taken to Hyundai Pinetown this year(2018) Fk70pmGp, it stayed there for about 16 weeks. I think I got it back last week of August 2018. Yesterday I discovered that my petrol pump have been changed with an old one which is even welded and I have been putting and loosing petrol quickly due to that but I only realised yesterday (23/11/2018) workshop manager acknowledged that pump is indeed not for my i20 and that exchange could have been done *******ly whilst the car was in their premises but they are refusing to fix it saying I must pay for that. I need hyundai Pinetown to fix it and refund my petrol money for the past 3 months. I have been a loyal hyundai Pinetown customer for more than 10 years and they are treating me like ****.