I bought a standard bumper for my series 3 to replace the big roo bar it came with. But, it won't fit.

One side is higher than the other so the upper and lower brackets, once slide onto the car, means the bumper is crooked. The roobar bumper just had an upper mount so could be spaced out to align it! Is the car wrong? Is the bumper wrong?

Bent dumb irons
Weak rotting dumb irons or
Badly replaced dumb irons.
It's one of them.