Can Strata Council place a lien on my townhouse for work not completed under a roofing contract they signed and and were responsible for?

Strata council contracted out a roofing project and hired a 'contractor' to oversee the work. Owners were not provided with a copy of the contract. I was informed by the Strata management that the contract included clean-up. I arrived home after the contractors had left, clean up had not been done at my townhouse and because of safety issues, I did the work myself. I left a message with the management company. I also left a large sign on the pile of debris I'd collected requesting it not be removed until reviewed with management it was irrespectively removed. The Strata Management company denies notification of issues including receipt of my telephone message. Having no response, I contacted the Strata Management company again stating that I was withholding 10% of my roofing levy because of contractor deficiencies. They requested details which I sent and included photographs. I received no further communication until a recent demand notice and threat of placing a lien on my townhouse.

Can they legally file a lien on my townhouse. Without incurring huge legal fees, how do I protect myself?