Loft company walked out!

Hello, I recently bought a property which I have been renovating for 6 months now. The final part is the loft conversion. I selected a company that would deal with the whole conversion as a project. The contract states that there is a penalty clause of £100 per day after the completion date given until the project is completed. My completion date was yesterday, but they are so far behind that it's actually 2 weeks more until completion. So yesterday the company said they refused to work on my property any longer, probably because they knew they were going to lose money. They won't put it in writing but they have not turned up to work there today. They don't answer my calls nor respond to voicemails, texts or emails. I have holes in the roof and only some of the floor is laid. HELP!

P.s. The company is called: UK Loft Conversions Ltd - stay well away from these cowboys!!

We have paid them in stages as per the contract, its difficult as they did not finish each stage before starting the next stage and its also difficult for me to know how much is yet to go. I.E, The dormer is up, but there are no windows fitted in. We haven't paid the entire amount but we have paid over half the stages worth.