Hi, I understand how stressful this situation must feel, and it's good that you're seeking clarity. If you pay the pending amount, the company is likely to issue the service letter as per their policies, but it may still indicate your termination due to the prior issue. During background verification (BGV) with other companies, this detail could surface if the new employer contacts them directly.
It's always advisable to be honest about your past and explain the circumstances positively while focusing on how you've grown since then. Many employers value integrity and transparency over past mistakes. You might also consider seeking legal advice or negotiating with the company for clarity on how they would present your exit in the letter.