Sorry for the delay in reply. I was stuck in an important issue.
Banking company means a company which is running bank .Bank can be in various forms
 Bank can be in the form of co-operative society also i.e it can be a co-operative bank.Bank can be a statutory body like SBI 
So Banking  work can be done in the form of many different types of legal entities. So when banking work is done my company it is called banking company.  Generally it is done by banking company also 
Financial Institutions you can think about NBFC’s and also government  run financial institutions .
Central statutory auditor  means the person who signs the main audit report , main financial statements .So Central statutory auditor is nothing but statutory auditor and others are called branch auditors.