I have cut my hours at work on the strength of a job offer in writing too advertised at jobcenter?

The lady then wrote me a letter saying that she didn't want me due to the hle of tax and insurance, I was going self employed and the hle ! would have been mine not hers! Her daughter works at jobcentre too, surely they must know cash in hand is illegal. I am upset and annoyed as I also paid extra (only �15) to have my car insured to ferry her about too, so I had it all done properly and feel now I have been penalised because of this. Should I tell my local jobcentre about this? and if I dont get cheque as promised for insurance should I tell them that too?