Is BMW really a trustworthy brand???

I purchased a bmw m5 in June 2015. I was told at the time by the sales manager himself the car had a newly fitted engine with a 2 year warranty. 5 months later I have problem with the car engine, when asking assistance on the warranty I am told that the warranty has conveniently expired in July 2015 (a month after the purchase). On top of this i bought a mechanical warranty. BMW at this present moment i own the following