Nashua is reaping me off

Have a contract for a photo copier with Nashua, had a complaint that the quality of copies was very poor due to drum unit needs to be replaced they sent someone who just wiped the machine and it's still doing the same thing they refused to replace it ,so I stopped paying now they sending me emails from their lawyers claiming 100 000 for breach of contract But they failed to keep their side of the contract Shame on them