You must not enter www in front of the domain name. In www.mumbaihosting.com only mumbaihosting.com is the domain name and in this case www is not a part of the domain name but indicates the computer resource name (see also the explanation of domain name).
If you do enter www you may receive a response that the domain name is available, even though it is taken.
You cannot search on subdomains either, since it is only the owner of the top-level domain who knows if the subdomain is available.
Dots in the search are only permitted as separators between top-level domains and subdomains.
Searches are made in the format SUBDOMAIN.TOP-LEVEL DOMAIN, e.g. mumbaihosting.com, tuborg.dk, rover.co.uk, ports.se etc.