Just a note since I was conned by bitumen bandits November last year. It was the classic, the front man had a strong British accent, they did the job but over measured up by heaps and it cost me an extra $600. On their invoice, the ABN belongs to somebody else or just a bogus person, they won't answer their phone, don't respond to texts and don't respond to emails. Luckily I took photo's of their truck and workers which I have passed on to authorities.
I suggest a read of this site https://www.facebook.com/StopTravellingConMen
I would say they change their business cards and invoice's depending on where they are targetting. If they turn up let the cops know they are in the area as they are continuously trying to apprehend them but they generally stay one step ahead.
These guys had a white truck with Queensland plates 344 TXT, plates were maroon on a white background.
Yes there are a quite a few getting around..mostly of Irish background and classes as "travellers".
Sorry to hear of your predicament but how did they get the extra $600 from you?
Would you mind explaining how they operate ?