What kind of a lawyer would I ask about an issue where a landlord has filed a claim with a collection agency on a charge I do not believe to be valid?

I terminated an apartment rental lease 3 and a half years ago. The landlord used my security deposit for the final month's rent. After moving out the landlord sent me a letter claiming damage. I responded with photographic proof that there was no damage, and heard nothing in response. In the subsequent time the property has been sold to new owners. Now I suddenly have received a bill from a collection agency for a claim filed 6 months ago, 3 years after I moved out. I want to fight this and am not sure whether to call a consumer, bankruptcy or real estate lawyer to deal with the collection agency.