Dear Philadelphia - you need to confer with a lawyer about liening the project to pressure the owner to pay. Depending on how much you are owed, you can sue or get a lawyer to sue for you. Do not wait - the mechanic's lien laws are very strict about time requirements - good luck.
From my years of construction experience, it seems like you may have a number of remedies. First, if this is a private project subject to the PA Prompt Pay Act, you can obtain attorneys fees and penalty interest, if the person is arbitrarily and vexatiously withholding this money. You also have the right to file a lien against the property that benefited for the work, but you are running out of time to do that. A lien can also catch the attention of the property owner because lenders and others who may have the property securing other debts take issue with liens. You also have your typical breach of contract claims. If this was a residential dwelling though and you did not comply with the home improvement contractor law, your remedies may be more limited, but you are still entitled to payment for the work and materials provided. you should send a letter to the party stating that you intend on taking some action unless paid by a date certain
This response is only general and preliminary in nature and is not intended to serve as any legal undertaking, representation or advice until all facts are disclosed and representation is formalized.