Shoddyjob, I too was in this situation last year. Paid a guy 3200 and there was bits that were bad but not as bad as yours at all. Had all the threats, all the worry. Took a week off work to sit in my house and make sure he didn't come back to do damage. Paid for a skip, scaff on top. Have just had to pay to have it all done again.
Citizens advice are useless. Police who were called were even more useless. Do not pay anymore.
It seems the rendering and roofing trade in particular have so many chancers and its terrible as there is hardly any comeback on them. A friend of mine took his roofer to court for doing 17k of damage. He won but won't get anything as he's been bankrupt several times.
All these guys cast a shadow on the good guys.
It's s**t being in this position mate, really worrying. Hang in there and don't give in.