Unreliable mechanical service

I received the worst experience from the Suzuki Brits branch.I took my car in as it had a distorting noise coming from the engine.Upon diagnosis I was told that they can't find any fault, however the sound persisted and I was told that they may need to strip the engine to do a full test.I took the car back for the stripping and boom I was told that I had voided the manufacturers warranty as they found that the oil cap was missing therefore that led to oil starvation,which is surprising because when they did the first diagnosis the oil cap was in place and the sound still occurred.I asked for footage showing that upon receiving the car there was no oil cap and guess what they don't have footage.They refused to fix my car after stripping the engine off.I collected my car with an engine in boxes and took it to a third party for assistance as I needed the car urgently.I have suffered a lot of financial constraints from fixing the car that was initially fumbed by the technician from the branch.I am no mechanic and have absolutely no idea with what happens with a car however I can tell when the is a strange thing happening with the car.I really feel that Suzuki Brits has failed me in terms of honesty and transparency on what transpired prior to my car being faulty.This is a brand new car that is only two years old ,however the issues I am experiencing with it are far and beyond.