Defective Notice

some has taken friendly loan from me 8 lakh.he has paid me 2 lakh. but he did not agree to reback balance amount. as a result there was huge arguments with him. at the end he has paid me 8 lakh rs cheque. But it was stopped payment. My lawyer has given legal notice demanding 6 lakh. The accused has replied and agreed to pay in installment. Now accused is saying its a defective notice so case should not continue. Now my lawyer does not getting any suitable court order for me.. pls help me. How and what should I do .