U/s 138 reply

i account manager in Real Estate. i was given chq of total amount to a customer against cancellation of plot. But due to insufficeint fund chq has dishonred . When customer was came again in my office we  given him another chq of half amount  and he assured me , he would return the previous chq . But second  chq rejected again. 

Now the customer has sent me notice u/s 138 & he include both chq amount in notice. what should i do, how to reply the notice.