Contractor filing suit against homeowner

[melissarenee]

What is the name of your state (only U.S. law)? PA
A few weeks ago, despite my better judgment I did some minor repairs for someone. The original contract was to replace a bathtub surround and some drywall work in the customer's bathroom. Once I started the project they requested that I replace the vanity and sink as well as the flooring. All of the extra work was completed on verbal agreement.
I purchased all remaining materials which were necessary to perform the work. While I was replacing the vanity I had advised the customer that it would be wise to replace some bad plumbing that they had. They chose not to. My contracts all state that payment is due upon completion and these people in addition to the labor also owe me for the materials that I have purchased. I received a letter from an attorney that they had apparently consulted with, stating that once he received the bill from a local plumber (that these people obviously had come in after me)...he would decide whether or not to file a claim against me.
I am curious if anyone has any experience with this sort of issue. I was never contacted by them, they never informed me if something I had done was wrong. which really could have only been a leak in the faucet or something as I never did any plumbing work at their residence. I plan on filing tomorrow at the District Magistrate because obviously they are refusing to pay me the money they owe.