OP, the vendor had a duty under a contract to supply you with services and wire at the agreed-upon rate. They then asked for an amendment to the contract because the job allegedly required more wire. This was false. You agreed to the original contract and are required to pay that. Any amendment requires the same elements of a valid contract, including consideration. Here, you were fraudulently induced into entering the amended contract and you will need to sue for the difference between the amended contract with fraudulent basis and the original contract. In addition, since the amount the provided was accounted for in the original, you could claim that they had a preexisting duty to perform the original contract. This preexisting duty rule can assist you in recovering the overpayment. Finally, if your state has a builder licensure requirement for residential construction, you may be able to use the licensure requirement as a sword if your law so allows.