Are there any non-profit organisations which help in filling citizenship application form so that we don't make any errors and our applications don't get returned?
Yes. There are settlement agencies which serve immigrants and could advise you on your citizenship application. If you're in Ontario, search here: http://www.settlement.org/findhelp/
Are there any non-profit organisations which help in filling citizenship application form so that we don't make any errors and our applications don't get returned?
The instruction guide is actually quite clear as to the requirements but many applicants rush through the application or disregard that CIC expect an explanation as to why a document has not been submitted. An example is the requirement to submit travel documents covering the 4 year qualifying residence period. Some applicants don't submit this either because the document is expired or they have one that does not cover the period. When CIC receive the application and don't see this document they send the package back as they assume the applicant failed to include it. Another common error is for applicants to submit documents that are not in English or French without translation. Make sure you are filling out the most recent version of the application form.