Seller refuses to pay Invoice amount citing quality issues,

Hello all, Case history: 1. 2016: In a trade deal happened between Seller and Buyer 2. 2016: Few lakhs worth of goods was sold and supplied 3. 2016: Seller raised objections in material quality and "refused to pay" the agreed amount , "after signing the Invoice". 4. 2017: Buyer approached police station about cheating case. Police did not file an FIR claiming some reasons. 5. 2017: Seller approached higher level officers, wrote RTI/questions. Everything on record. Also, Buyer failed reply to one letter by police. 6. 2018: Police inaction prompted Seller to file a case in Mumbai, under section 156(3). 7. Case is in a document verification stage, etc. Queries: 8. Have you worked under this section 156(3) case ever? 9. If not, have you worked in a similar case? 10. Will you be able to provide your fees and expenses to take over this case? "PLEASE REPLY to Q8/Q9/Q10",We will promptly connect with you at your number. Regards.