Failure to reply to AO regarding Condonation of delay u/s 119(2)(b)

i have a client who made an application u/s 119(2)(b) for filling return for refund claim. the AO send a notice to produce necessary documents. this notice was send by post but owing to the rurality of my client's area, the post reached nearly a month after the notice was issued by which time the time limit of 15 days was passed by nearly a month. Should i respond with an apology letter? please advice....

Thank you for your valuable advice