Argh, had the same problem when my grandma needed the roof work. I couldn't control it, because I was studying in another country and I was just sending the money. Those people were delaying the work and overcharged my grandma. Making a new excuse every time. And disappearing for several days from time to time without any notice. Once they finally finished the work, there was a problem with missing nails in few places which was discovered after a windy day. And then we had to ask a friend to nail the areas. Seriously, are all the construction workers so corrupted these days?
Strangely enough, that party of workers was also recommend to us by a neighbour xD.
I hope this will end up good for you and the гnscrupulous party will be punished.