If it sounds too good to be true then it probably is!
They can not write off your debt.
At best they can have it declared unenforceable meaning the lender cannot take you to court for a court order and have a judgement made against you (assuming they help defend your case) based on the consumer credit agreement (CCA) not meeting the requirements set out by the CCA ACT 1974.
Going down the route of getting your CCA and getting it declared unenforceable is a long and painful process, which this company may help you with, but there will still be lots of debt collection agencies willing to chase you for this debt until it is settled and beyond.
So you've got to ask yourself a question:
Do you feel lucky?