knowing exactly what Download Festival is(for non UK escapists) and why that being part of your future plans would piss her would certainly help. As for helping you deal with your predicament. Aren't there shelters for people that are homeless(regardless of how they came to be that way) you could seek a bed in one of those or whenever you find a job explain your situation to who ever employs you and see if they'd be willing to let you take refuge there(in their buisness) outside of regular work hours. Alternatively you could find a place to stow your stuff and squat infront of or near your house (and carry a sign explaining the dick move that your mum pulled)