Mechanic Lien was filed against my home?

I am a home owner in state of New York. I had new boilers in my basement last year and paid in full in cash to the plumber. Today I got the certified letter from a lawyer of a construction company notifying me that the mechanic lien was filed against my house because the plumber did not pay the supply company for the boilers and materials. I did not know the plumber did not pay them until now. What can I or should I do? The plumber has not returned the call. How can they file a mechanic lien against my home, although I had paid in full to the Plumber for the work and material last year? Can't the supply company go after the plumber?