Cheque stolen, tampered and cleared

I had issued a cheque on my account in Bombay Mercantile Bank for Rs. 8 lakhs in favour of my name to be deposited in my another bank account in HDFC Bank. I had dropped the cheque in HDFC Bank’s Drop box. However, the amount had not been credited to my account. After verifying records with BMC bank, we discovered that it had been credited to an unknown person. After clarifying with HDFC Bank, it was found that there was an incidence of a break in and there was theft of cheques from the drop box. The cheque was stolen from the custody of HDFC Bank & misused by a third-party. The amount was debited from my BMC account even though the cheque was altered as per image copy of my cheque. We submitted our complaint to RBI Ombudsman for justice but after 4 months we received the reply stating that this doesn’t come under their purview. Please advice what should be our next step as the amount is quite substantial for us. Thank you.