Am I liable for the debt if I don't dispute it in 30 days?

The FDCPA (§1692g(c)) says failure to file a dispute does not allow a court to assume you admit liability for the debt. However, being able to establish that you did comply with all statutory requirements may greatly enhance your chances of success. Your goal is to establish the facts and convince the judge or others who decide the matter that you are credible and deserve to have the law applied with its full effect on your behalf.