The more line you get, the more proof of income you need to present. You can't force them to grant your request. If they don't want, then the other company is always open to you.
What a credit investigator looks for more than the balance of a passbook is how money moves in terms of deposits and withdrawals over a longer period of time where it could establish a trend. 2 months may not be sufficient to check the trend of the movement of money and may not be a good basis for determining your credit worthiness.
Try to submit a more established document which would show that you would be able to sustain an additional plan like a credit card statement (where it would show that you have not maxed out of your credit limit) or an Income Tax Return (where your income could be established and compared to the plans you are sustaining) or proof of regular remittances and other established sources of income or a bank passbook with a longer account history (the longer the better).