Damaged pipe

Having a leaky roof fixed on my house today and the roofer offered to get rid of the ivy on the wall for a small extra cost. Great! Have been meaning to get that done for ages.

Paid him and off they went. did the washing up and the water ended up in the cupboard below the kitchen sink. They'd only gone and dislodged the waste water pipe. He now says that cant be down to him! Really? Says he will get hold of a plumber. I feel a dispute about who pays coming on