Was your bank document was officially (bank) certified one ? How much old the account was? you can also draw your financial plan, based on realistic facts and figures and try to satisfy the IO.
The account was from July to the last 4 months, because thats when i applied. The bank statements were from a bank, so they were certified. Shall i just send them a letter from my bank explaining that this is certified and that I can pay for the expenses for my stay in Canada?
It should be an official certification from the bank which includes when the account was opened and how much current balance it has. If you gave certificate of only the last four months then they could suspect that you just made the deposit, in a way built the account within the last four months, for the sole purpose of supporting your application.