Agency Commission Recovery-no Formal Agency Agreement Exists

My father has been working as a selling agent for a Tamil Nadu-based textile firm for over 15 years, operating under our agency based in Guwahati. We handled marketing, order procurement, and payment collections for their lungi products, against a 2% pre-GST commission on sales. Over the last 3 years, commissions amounting to approximately ₹5.4 lakhs accrued, out of which only ₹25,000 has been paid and ₹49,140 adjusted informally. No TDS has been filed on our PAN during this period. Additionally, our commission account was wrongfully debited with party balances, which we were never legally obligated to collect. In September 2024, my father personally travelled to Chennai, spending ₹26,000 to settle the issue, but no resolution followed. We have agent-signed sale copies, WhatsApp communication, and call recordings to prove the agency relationship. We're now exploring legal remedies (civil and criminal) and would like advice on how strong our case is and the best course of action.