landlord ripped me off

[spenrod]

I recently moved out of my room that i was renting in an HMO (house of multiple occupancy). We agreed when i moved in that the minimum stay was six months, i stayed for just over 7 months. i gave him a months notice when i was moving out and everything was fine. there was no damage caused to the room and no late payments of rent. However, there was never any paperwork signed and after i left i phoned him to arrange picking up my deposit and he told me i can't have it, when i asked y he said i broke the terms of the contract (the phantom contract). he said that as soon as i went over the first 6 months i automatically went into another 6 month agreement which was never mentioned hes plainly just ripping me off. I have done some research and I have found that he has not licensed the adress as an HMO and that he is definately not declaring any of his rent cash to inland revenue. i keep phoning different services and they keep sending me back and fourth to each other. I'm not 100% bothered about the cash i just don't want him to keep taking advantage of people. does anyone know where i should start???????