You think you have proved it to them because others back you up, have you not considered that they are just as wrong as you are in their belief?
You have no idea what the chance of getting a particular piece of material,gem, rune piece, or sundries when attacking/banishing, they do not publish these,therefore you can prove nothing with your, I did this ,we did this, and didn't get what we wanted, feel we should have got.
A sequence of we didn't get, doesn't mean there's a fault, each attack has the same chance each time, there is no I've done thousands I should have got at least one by now, the game doesn't know wether you have done one before, or any number of thousands one after the other.
I am not saying things don't mafunction,but have to say that they do err on the mean side, but what you expect,?They want your money and have a captive audience.