Manipulation in Cheque issued

Dear Experts here My brother had a shop in our area and done some business transaction with one of his items supplier in 2015. As a guarantee to the initial purchase he given 2 cheques dated June 2015. but before the expiry date of the cheques, he settled the first bill and unfortunately forgot to collect his cheques from the supplier. 2-3 months back in April-May 2016, while he shutdown his business due to loss, he had some dispute with supplier on discount on brother not ready to pay full amount since the supplier was not ready to give discount as promised earlier. He was ready to settle the bill if he get the discount as agreed by the supplier earlier. Now the supplier corrected the dates in the old cheques and send it to the bank for encashment. Bank rejected because of insufficient fund. Now they send one vakil notice to him asking full amount with legal fee. We approached bank authorities and they have given the scanned copy of cheques and it is very clear that they have done correction in the dates on the cheques. We are ready to pay full bill amount after agreed discount. Please let me know whether any possibility to approach any legal authority on manipulation of cheques against this supplier. Moreover, there are 5-6 cheques he already given to other suppliers after the above cheques and those are cleared in 2015 itself. Please help me by giving your advice whether we can approach a legal authority on manipulation of cheques Regards Shafeek