@Devyani Dey , I used digwebinterface to look up the sub domains. Most have A records pointing to 103.53.43.82, while webmail.e-gyaan.com has a CNAME pointing to your e-gyaan.com, which I'm assuming you may want to keep.
nslookup
shows the bigrock.in as the DNS registrar. You will need to login to that registrar to remove the subdomain and A records.