If you've acted as a guarantor for a bank loan and the borrower has defaulted, leading to an NPA and damage to your credit score, you have legal options. You can pursue a recovery suit against the defaulting borrower to recoup your losses. While directly suing the Chartered Accountant (CA) might be difficult without evidence of complicity, you may be able to include them as a defendant if you have proof of their involvement. Seeking legal advice from a local lawyer is recommended to navigate this complex situation and protect your interests.