You might be able to get the £49.50 back. First you should dispute the charge with the "broker". Assuming that they wont find you a loan in your present circumstances (i.e. without a guarantor), you are entitled to a refund. If they refuse, you should contact your bank and ask them to start their disputes process to reverse the payment.
It would be best, in my view, to be honest with the estate agent about what has happened as otherwise they will view more dimly the broken promise.
In my view you should not try to borrow money in your circumstances. If you are struggling to pay your rent, even if you could, borrowing £2000 and repaying £3000 will be £1000 wasted and it will mean that your financial problems today will become even greater financial problems in the future. You should do what is necessary to put your finances in order. It may be worth visiting a debt adviser at your local Citizens Advice Bureau.