As Blackduck said, try their solicitors, especially if they signed the paperwork stating they would leave it clear.
That said, when we bought our house it was left FULL of crap. I mean full. Plus there was 20ft at the end of the house that was literally a rubbish tip. We dug 2 tonnes of stuff out of there. And his solicitors didn't have a forwarding address, so all we could do was withhold payment for the appliances (he'd wanted 50 quid for the washing machine. He didn't get it).