I have been blacklisted from a refinery, how do i find out why?

Where are you?
Have you any background issues or judgments?
Refused gun permit or bank loan?
Wanted for law infractions?
Are you authorized to work in the country?

i am in the UK , i worked for the refinery before but had an issue with a sub contractor i was with and lost my job. although i done nothing against the refinery they still stopped me working for another contractor. it does happen a lot in this country and is illegal but they always find a way round it