Poor workmanship- Ruined the roofing by the tradespeople selected here

I have posted to do small vestibule/sunroom (2.5cm x2.5cm) in rated people for less than quote of £15,000 and I got a couple of quotes and selected one from that to start asap that was not very cheap. The trades person initially given the drawing of pitched roof with more than 20 degree, but he finished with flat roof with less than 4 degree with light weight roof tiles and roof window used for pitched roof, also the tiles are not extending enough out to the edges on to the gutter and installed plastic lead to fix the window. I do not mind having flat roof, but he did not install flat roof with flat roof materials and he never followed the installation guide. I called my roofer (Buckstone roofing in Edinburgh) to check the roofing, they were finding this issues of using incorrect materials and poor workmanship. I received quote for over £3,000 to correct and complete the roof from other roofers. I paid everything to this tradesperson except balance of £1,000. I sent him an email explaining everything, but he did not respond me and he did not even removing the rubbish. Could you please advice me what options available to me to correct and complete the work without involving additional cost. Thanks in advance.