OPTION A - Firstly give a small listing in the local newspaper and a national daily rgrding loss of certificates. Contact your school, submit an application stating loss of certificates. Mention which year you passed out and Roll Nos.Attach a xerox copy of the Newspaper Listing. Preferably add some id proof . The school will authenticate it and the prinicpal will sign and put his seal on it. Forward it to the ICSE board in Delhi.
You can also e mail your query to the ICSE on their e mail id
Forget the old one, appear again and pass with flying colors