You should consult with an experienced construction litigation attorney in your area to review your construction contract and discuss the facts in more detail. From what you say, you appear to have a reasonably good chance of prevailing in a contract dispute with your general contractor. Most construction contracts provide for a change order process and if you did not mutually depart from that process then you should be protected from unauthorized change orders. Allowances for items like fixtures and carpet are normally merely estimates and the contract usually makes the owner responsible for the actual cost of allowance items. An unconditional contractor affidavit issued at closing provides important protections for the owner, but adding conditions and exceptions to the affidavit can limit the value of the affidavit. Withholding retainage to pay for incomplete punchlist items can also complicate the legal picture. If there are unpaid subs and suppliers you may end up with mechanics' liens on your property and of course the general contractor may also try to file a lien. You can also file a complaint with the Georgia Board of Residential and General Contractors at the link I have provided.
Your situation is, unfortunately, quite common in residential construction. I am handling a case right now where a contractor told an owner of a long list of "extras" that were only identified as such after the work was long done, and even after the contractor filed a lien and lawsuit. An experienced construction attorney will know a number of ways to defend these cases based on what the contract says, what an affidavit or waiver says, and the circumstances of the project.
A major problem and the source of many of these disputes is that there can be circumstances where the parties, by their conduct, depart from the formal written terms of the agreement and may engage in informal procedures. For example, if there are any instances where you asked for or consented to an extra work item and an extra charge, however small, that may give the contractor a basis to argue that it set the pattern that both parties could depart from the formal change order procedure.
Your situation is complicated by the claims of subs and suppliers. You have a right to demand that your contractor give you a full accounting of who he has paid and who he owes; then, potentially, you will have to deal with claims asserted by these other persons as well. The best way to avoid such claims is to have a procedure from the start of the project where the contractor identifies his subs and suppliers and shows you evidence they have been paid as a condition to getting his next draw. That way, you manage the money and hang on to what you may need.
The construction attorney you select will have to get into the specifics in detail with you so keep in mind the size of the problem; a lot matters on how much the GC is asking for and how much emerges in the way of claims by others. Don't make any more payments until you consult with legal counsel. Good luck.
You have been given good information so far. Rather than repeat that information, let me make clear, you need to have specific advice from a knowledgeable construction attorney regarding your situation which will require reviewing the actual contract and the other forms as well as the facts. You will need assistance in drafting a response, understanding the risk of legal action to collect that the contractor may file if not paid (and your defenses) and whether a complaint would be appropriate to the state contractor licensing board.
Disclosure: This answer and any information contained in this answer is not intended to be treated as legal advice. It is for informational purposes to educate about legal issues. You should contact an attorney for specific legal advice for your situation. Specific legal advice based on full knowledge of your specific situation and all facts may differ from general information. This posting does not create an attorney-client relationship or privilege of any kind. This attorney actively licensed only in the State of Georgia. If this is a Georgia matter, you may of course contact me to discuss possible representation. FEEDBACK: Both AVVO and other readers are interested in your feedback on the quality of the answers. Please check the “thumbs up” symbol if you find an answer helpful.