Based on the limited information, and absent making a compelling argument to whoever is trying to collect on the forged document, you will probably have to file suit to prove you didn't sign the document.
You may have claims for fraud, or claims to be excused from operation of the documents. But you also may have to pay for the service work, if you actually ordered the work, authorized it, and had knowledge that it was being done. You need to sit with counsel for a full interview and review of your rights and responsibilities.
Go see an attorney right away. Don't wait for them to take action. A declaratory judgment action may be appropriate.
This response is based on information provided. Many variables may exist that can only be addressed in an interview. This answer in no way creates an attorney-client relationship.