If you've received a false cheque notice and have already made the payment via RTGS, you have grounds to contest the notices. You should reply to both notices, detailing the payment made, and can consider filing a civil suit for specific performance if the seller is refusing to proceed with the sale deed. While some suggest defamation is possible, legal advice indicates that responding correctly to the notices is the primary step, and filing a premature defamation case might weaken your defence.